A 20 foot extension ladder liens against a building if the base of the latter is placed 6 feet from the base of the building what is the angle of elevation of the latter

For this problem, you're going to need to use trig. More specifically, you need to use the tangent function:

tan (value) = opposite/adjacent

tan 75 = opposite/8 (Here, the opposite side is the length of the ladder)

8 * tan 75 = opposite

29.8564065 = opposite

So, the ladder is 29.9 feet.