This is for my school city, and a test worth half my grade

Question

A 41-foot ladder is placed against a vertical wall of an apartment building. The base of the ladder is 9 feet from the base of the apartment building. How many feet up the apartment building is the top of the ladder?

1. 
   

Answer 1

h^2 = 41^2 - 9^2 = 1681 -81 = 1600

h =sqr1600 = 40 feet high