b. 25 cos(56)
You have a right triangle whose hypotenuse is 25 ft, the given angle is 34 degrees and you want to know the length of the opposite side. The immediate obvious answer is 25 sin(34). But that is not one of the available answers. So you use the symmetric property of sin and cos. Namely sin(a) = cos(90-a).
90 - 34 = 56.
So the answer is 25 cos(56)
