The UN says $6B from the world's billionaires could solve a hunger crisis. Elon Musk says he will sell Tesla stock and donate proceeds if the UN can prove that.

David Beasley, the director of the UN's World Food Programme, issued a recent plea to billionaires.

He said $6 billion would help 42 million who were "literally going to die if we don't reach them."

The world's richest man, Elon Musk, says he'll act if the UN could show the math behind the figure.

The billionaire Elon Musk said he'd sell Tesla stock and donate the proceeds if the UN could prove that just a tiny percentage of his wealth could save tens of millions of lives.

Musk was responding to comments by David Beasley, the director of the UN's World Food Programme, who told CNN's "Connect the World" last week that a $6 billion donation from billionaires such as Musk and Jeff Bezos could help 42 million people who he said were "literally going to die if we don't reach them."

Musk is the world's richest man and recently became the first person in the Bloomberg Billionaires Index ever to have an estimated net worth north of $300 billion.

The index currently lists the Tesla CEO's net worth at $311 billion, meaning $6 billion would be 2% of his wealth. Such a donation would still leave him besting the world's second-richest person, Bezos, by at least $100 billion. Both men's net worth consists largely of stock in companies they founded.

But Musk is challenging the claim that the specific amount will solve the hunger crisis, saying on Twitter that if the World Food Programme could show its math, then he would "sell Tesla stock right now and do it." He also demanded transparency about how the money would be spent.