A motion detector at the corner of a building can detect motion outside within a radius of 20 feet. Within what area can it detect motion? The building takes up ¼ of the circle

Astick 2 m long is placed vertically at point b. the top of the stick is in line with the top of a tree as seen from point a, which is 3 m from the stick and 30 m from the tree. how tall is the tree?