150K x 43 = 6,450,000.
I'm guessing that there is a fair chance that at least one of the 43 companies alone will allow them to break even on their investment. They should end up doing extremely well on the deal.
Numbers missing: what is the typical valuation at Series A for a company coming out of YC? If it's $2 million then he'll wind up with (on average) 7.5% of each company (similar to what YC itself gets for about eight times less money), so to break even on one exit it'll have to be a $100+ million exit, which would be bigger than any YC exit so far as far as I know.