Exhibit (c)(21)

PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Project Francis Conflicts Committee GP LLC Discussion Materials of the Board of Directors of Arkose June 1, 2018 PRIVATE AND CONFIDENTIAL. This document is being sent to you for your information only as an investment banking client of Gol dman Sachs and should not be forwarded outside of your organization. This document has been prepared by the Investment Banking Division and is not a produ ct of Goldman Sachs Global Investment Research. This document should not be used as a basis for trading in the securities or loans of the companies name d herein or for any other investment decision. This document does not constitute an offer to sell the securities or loans of the companies named herein or a solic itation of proxies or votes and should not be construed as consisting of investment advice. Goldman Sachs does not provide accounting, tax, or legal advice.

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PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Disclaimer These materials have been prepared and are provided by Goldman Sachs on a confidential basis solely for the information and assistance of the Conflicts Committee of Board of Directors of Arkose GP LLC (the “Committee"), the general partner of Arkose GP LP (the "Company"), in connection with its consideration of the matters referred to herein. These materials and Goldman Sachs’ presentation relating to these materials (the “Confidential Information”) may not be disclosed to any third party or circulated or referred to publicly or used for or relied upon for any other purpose without the prior written consent of Goldman Sachs. The Confidential Information was not prepared with a view to public disclosure or to conform to any disclosure standards under any state, federal or international securities laws or other laws, rules or regulations, and Goldman Sachs does not take any responsibility for the use of the Confidential Information by persons other than those set forth above. Notwithstanding anything in this Confidential Information to the contrary, the Company may disclose to any person the US federal income and state income tax treatment and tax structure of any transaction described herein and all materials of any kind (including tax opinions and other tax analyses) that are provided to the Company relating to such tax treatment and tax structure, without Goldman Sachs imposing any limitation of any kind. The Confidential Information has been prepared by the Investment Banking Division of Goldman Sachs and is not a product of its research department. Goldman Sachs and its affiliates are engaged in advisory, underwriting and financing, principal investing, sales and trading, research, investment management and other financial and non-financial activities and services for various persons and entities. Goldman Sachs and its affiliates and employees, and funds or other entities they manage or in which they invest or have other economic interests or with which they co-invest, may at any time purchase, sell, hold or vote long or short positions and investments in securities, derivatives, loans, commodities, currencies, credit default swaps and other financial instruments of the Company, any other party to any transaction and any of their respective affiliates or any currency or commodity that may be involved in any transaction. Goldman Sachs’ investment banking division maintains regular, ordinary course client service dialogues with clients and potential clients to review events, opportunities, and conditions in particular sectors and industries and, in that connection, Goldman Sachs may make reference to the Company, but Goldman Sachs will not disclose any confidential information received from the Company. The Confidential Information has been prepared based on historical financial information, forecasts and other information obtained by Goldman Sachs from publicly available sources, the management of the Company or other sources (approved for our use by the Company in the case of information from management and non-public information). 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The analyses contained in the Confidential Information do not purport to be appraisals nor do they necessarily reflect the prices at which businesses or securities actually may be sold or purchased. Goldman Sachs’ role in any due diligence review is limited solely to performing such a review as it shall deem necessary to support its own advice and analysis and shall not be on behalf of the Company. Analyses based upon forecasts of future results are not necessarily indicative of actual future results, which may be significantly more or less favorable than suggested by these analyses, and Goldman Sachs does not assume responsibility if future results are materially different from those forecast. The Confidential Information does not address the underlying business decision of the Company to engage in any transaction, or the relative merits of any transaction or strategic alternative referred to herein as compared to any other transaction or alternative that may be available to the Company. The Confidential Information is necessarily based on economic, monetary, market and other conditions as in effect on, and the information made available to Goldman Sachs as of, the date of such Confidential Information and Goldman Sachs assumes no responsibility for updating or revising the Confidential Information based on circumstances, developments or events occurring after such date. The Confidential Information does not constitute any opinion, nor does the Confidential Information constitute a recommendation to the Committee, any security holder of the Company or any other person as to how to vote or act with respect to any transaction or any other matter. The Confidential Information, including this disclaimer, is subject to, and governed by, any written agreement between the Company and the Committee, on the one hand, and Goldman Sachs, on the other hand. 1

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PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Illustrative Series B Settlement at Prices Various Assumed GP ($ in millions) Share Trading Day VWAP Spot 5-Day 10-Day 15-Day 20-Day 30-Day 60-Day Series B Value (@ 4.5% Series B Take) 1.6 x Exchange Ratio 1.7 x Exchange Ratio 1.8 x Exchange Ratio GP Shares Issued for Series B Units 1.6 x Exchange Ratio 1.7 x Exchange Ratio 1.8 x Exchange Ratio $ 332 348 365 $ 319 335 351 $ 316 331 347 $ 310 326 341 $ 306 321 336 $ 299 314 329 $ 282 296 310 17.2 18.1 18.9 17.1 17.9 18.8 17.1 17.9 18.7 17.0 17.8 18.7 16.9 17.8 18.6 16.8 17.7 18.5 16.6 17.5 18.3 Illustrative Share Price Appreciation Spot 5 % 10 % 15 % 20 % 25 % 30 % Series B Value (@ 4.5% Series B Take) 1.6 x Exchange Ratio 1.7 x Exchange Ratio 1.8 x Exchange Ratio GP Shares Issued for Series B Units 1.6 x Exchange Ratio 1.7 x Exchange Ratio 1.8 x Exchange Ratio $ 332 348 365 $ 353 370 387 $ 374 392 410 $ 395 414 433 $ 416 436 455 $ 437 458 478 $ 459 480 501 17.2 18.1 18.9 17.5 18.3 19.2 17.7 18.5 19.4 17.9 18.7 19.5 18.0 18.9 19.7 18.2 19.0 19.9 18.3 19.2 20.0 Source: Arkose Projections, Wall Street research and Bloomberg market data as of 31-May-2018 1 Excludes Series B Conversion 2 Assumed GP Share Price $ 19.25 $ 20.21 $ 21.18 $ 22.14 $ 23.10 $ 24.06 $ 25.03 Assumed GP Share Price $ 19.25 $ 18.67 $ 18.51 $ 18.27 $ 18.06 $ 17.75 $ 16.96

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