Answer: B. 17
Explanation:
Mostly just common sense to me. The first triangle is visibly bigger than the second one, and given the comparison between the 50° and 45° we can also assume that that side will be greater than 15. This eliminates A, C, and D.
But, the way I would do this is divide 50 by 45 to see the relationship between the sides. 50/45 = 1.111111111
15 · 1.111111111 = 16.66666667
You could probably round this 17, and since it says a possible length, that would be okay and the closest answer.
Hopes this helps!