Actually, you could solve world hunger for free, by destroying the system that creates it, and fairly distributing the food already being produced

But even if you look at actually tackling it within capitalism, I was basing my estimation on when the UN told Musk it would take 6 billion.
That link confirms that that figure is out of date, but yours is still off Current estimates suggest that as of this year, we need donor governments to invest around $37 billion every year until 2030 to tackle both extreme and chronic hunger

That really is pocket change if they split it between them, even just the top 5 or even ten richest, let alone all of them.
They choose not to