Question

Janet wants to measure the height of her apartment building. She places a pocket mirror on the ground 20 ft from the building and steps backwards until she can see the top of the build in the mirror. She is 18 in from the mirror and her eyes are 5 ft 3 in above the ground. The angle formed by her line of sight and the ground is congruent to the angle formed by the reflection of the building and the ground. How tall is the building?

Answer 1

Here, we know, tan Ф = P / B
As both angles are equal, ratio would be equal.
P1 / B1 = P2 / B2

Here, P1 = 5 ft 3 in. 5 1/4 = 21/4 ft
B1 = 1 1/2 = 3/2 ft
B2 = 20 ft

Substitute the values, 
P2 / 20 = 21/4 / 3/2
P2 / 20 = 21/4 * 2/3
P2 /20 = 7/2
P2 = 20/2 * 7
P2 = 10 * 7
P2 = 70 Ft

In short, Your Answer would be 70 Feet

Hope this helps!