Fence calc problem

Question

A fence 7 feet tall runs parallel to a tall building at a distance of 4 feet from the building.

What is the length of the shortest ladder that will reach from the ground over the fence to the wall of the building?

Answer 1

Rather than re-create a video for this problem, here is a link to one which is almost identical to yours:

https://www.youtube.com/watch?v=n09mdFU3HsU

(copy/paste that link into your Web browser)

He solves it step-by-step.