Answer:
See image
Explanation:
Look at the front side of the building. It's a triangle, with the height given. We can see a right triangle here which means we can use the Pythagorean theorem. a^2 + b^2 = c^2 (a and b are the shorter sides called legs and c is the longest side called the hypotenuse)
20^2 + 13^2 = c^2
400 + 169 = c^2
569 = c^2 square root both sides
Sqrt 569 is approximately 23.85 ft. This is the length from the roof peak down the front edge to the bottom front right corner in the image.
Now, if we consider the roof itself. That edge is now a leg (on the front face it was the hypotenuse). The other leg is the 35 ft width given. So we'll use pythagorean theorem again to find the diagonal
23.85^2 + 35^2 = c^2
568.8 + 1225 = c^2
1793.8 = c^2
Square root both sides of the equation.
Sqrt 1793.8 = c
42.35 ft = c
The diagonal of the roof is just over 42 feet, that is 42.35 feet.