Originally posted on Arqade. This question was posted by another user on Arqade due to being a game, which is correct. However due to the lack of attention this question has garnered so far I decided to post it at the home of the puzzlers.
The issue is that the question doesn't seem to be solved mathematically, as the original poster claims the answer is not 16, when mathematically it should be 16.
3x = 24 <=> x = 8
x + y = 25 <=> y = 17
y + z = 8 <=> z = -9
x+y+z = ? = 16