In my opinion, I think it would be -4. Why, i do not know I think I have done this problem like a very long time ago. So, I am sorry if this does not help you any!
it would have to be a, because using pythagorean theorem, we can find that a squared + b squared = c squared. substitute that for 1 + b squared = 4; b squared=3 b = square root of 3
