Answer:
D: 25 miles
Step-by-step explanation:
Pythagorean Theorem:

36^2 + b^2 = 39^2
1,296 + b^2 = 1,521
b^2 = 225
b = 25
For the cylinder on the left-hand-side,

now, for the triangular prism on the right-hand-side,
notice is really just 2 triangles and 3 rectangles, stacked up to each other at the edges.
the triangles have a base of 4, and a height of 1.5.
the rectangle on the left and the one on the right is a 6x2.5 rectangle.
the rectangle at the bottom, is a 4x6 rectangle.
adding their areas, is the area of the prism,
X=6, just subtract the 2x from both sides and you would have 2x - 5 = 7
then add the 5 to both sides which equals 2x = 12
then finally divide by 2 and get x = 6