You should use the law of cosines because since you are given two sides and an angle that IS included, this is not enough information to use the law of sines (the angle would need to be non-included):
c = √(a2+b2-2ab·cosθ)
c = √(302+502-2(30·50·cos25°)) ≈ 26.1ft
Hence, the missing side is about 26.1 feet. Hope this helped!