The correct answer is 14 ... the frog counted what it saw and it saw 5, 2, 7 unicorns.
Edit: I do see now that "He saw" kind of messes the question up. My intent would have been better expressed with "There were". But again this proves my point! GPT4 is able to (most of the time) correctly work through the poor wording and interpret the question the way I meant it, and I think the way most people would read it.