Answer:
1) From the measure of 40°, you can write:
tan(40°) = 100/x, where x is the base from the building to the tower
⇒x=100/tan(40°) = 119,18 m
2) From the measure of 30°, you can write
tan(30°) = y / 119,18, where y is the height from the roof of Jill's building to the top of the tower.
Then, y = tan(30°) * 119,18 = 68,81 m
3) The height of Jill's building is 100 - 68,81 = 31,19 m
