Question

Jill is standing at the base of her apartment building. She measures the angle of elevation to the top of a nearby tower to be 40º. Then Jill goes to the roof of her apartment building, directly above her previous position, and measures the angle of elevation to the top of the same tower to be 30°.
If the height of the tower is 100 meters, the height of Jill's apartment building is (answer here) meters.

Answer 1

Let the distance of Jill form the base of the tower be x, then tan 40 = 100/x
x = 100/tan 40 = 100/0.8391 = 119.18 meters

Let the height of the tower from the level of the top of Jill's apartment be y, then tan 30 = y/119.18
y = 119.18 x tan 30 = 68.8 meters

Therefore, the height of Jill's apartment is 100 - 68.8 = 31.2 meters