With all due respect, I would argue that this problem is not sufficiently defined. For example, what are the blinds, what did the small blind bet, and what is the small blind's range? If the small blind has a range of K5 or equivalent or better, or roughly the best 40% of all hands, according to Poker Cruncher, a 78 unsuited would have a 36% chance against that range. Assuming the big blind's positional advantage adds 5%, that would put the big blind's chances at 41%. That would not be enough to raise, unless the big blind is simply trying to make a play, is a superior player, or has reason to believe that the small blind folds too much.
Some of these issues are covered in my new book Hold'em Poker Super Strategy, available through Amazon.
Hope this helps.
Best regards
Norman Zadeh, Ph.D.