Musk’s $21 Billion Mystery: Where’s the Cash for Twitter? (2)

Elon Musk and Twitter Inc.reached an agreement for the world’s richest man to buy the social networking platform for $44 billion, resolving the pressing question of whether the company’s board would consent to the leveraged buyout deal.

On Musk’s side, though, there remains a mystery: How is he going to cover the $21 billion equity portion of the transaction that he’s personally guaranteed?

Musk, 50, has outlined the $13 billion in bank financing secured by the social-media company and the $12.5 billion backed by a pledge of some of his $170 billion Tesla Inc. stake. But he’s been short ...