Remember Soh Cah Toa (say it aloud, this is how I remember it)- Sin(a)=Opposite/Hypotenuse, Cos(a)=Adjacent/Hypotenuse, and Tan(a)=Opposite/Adjacent. Each of these terms is related to the angle you're working with
So for your problem:
3 ft is opposite of the angle so to calculate the hypotenuse=3/Sin(25)