Suppose you post your first hand (i.e. no reads) at a table in CO with a 100BB stack and flop middle set and top pair in an unraised pot (5 to flop) - board is something like J84 rainbow. It's checked to you and you pot it. UTG then re-raises pot. There are now 30BB in the pot. Calling costs 15, you have 94 left.

How big would his stack have to be to consider folding?