Ok, so this question is from seriously hard IQ test that has been doing the rounds on facebook, ok, 17 questions are easy 3 are hellishly hard, The answer to this one is 17, I do not know why, I found out by trial and error just to test, but It's killing me, anyone know why?
Note that $1+3+4+9=17$ and $1+7+1+0=9$.