This is a real life problem. We wish to add a ten foot diameter shade umbrella to our "tree" house which is a 6 feet by 6 feet square platform built on the stump of a dead oak tree in our back yard. The platform has a three foot tall wall around the perimeter. How high up does the top of the umbrella have to be to ensure that when it opens, it will not get caught on the rails? (1 Point)
