A ladder is resting against a wall. The top of the ladder touches the wall at a height of 20ft. Find the length of the ladder if its length is 4 ft more than its distance from the wall.
Use your good old Pythagorean theorem:
H = 20
L = D+4
L^2 = H^2 + D^2
(D+4)^2 = 20^2 + D^2
D^2 + 8D + 16 = 400 + D^2
8D = 384
D = 48
L = 52 ft