Security Robot

I truly enjoyed this problem. Although perhaps it is ambiguous - that is is there enough evidence that the answer has to be 7 - or can another code fit a different solution? There is a problem we look at that emphasizes this, states 11X11=4, 22X22=16, 33X33=? - there are multiple solutions that can be justified! Thus the problem does not have proper bounds... so one could state for your problem, for example, that the answer is 9 (although not on the list), the reasoning - take the number robot gives you, count number of straight lines in the number (depending on how it is written - 1 has one, 2 has 1, 3 has 0, 4 has 3, 5 has 2...) and multiply this by 3. Thus 12 = 2 straight lines in total times 3 giving 6, finally then 15 has 3 straight lines times 3 giving 9... again since 9 is not on multiple choice list, this logic eliminated. But I bet someone out there can think and justify of a reason other than number of letters in word, that one of multiple choice answers is the answer!