A 13-foot ladder is leaning against a vertical wall (see figure) when Jack begins pulling the foot

Question:

A 13-foot ladder is leaning against a vertical wall (see figure) when Jack begins pulling the foot of the ladder away from the wall at a rate of 0.5 ft/s. How fast is the top of the ladder sliding down the wall when the foot of the ladder is 5 ft from the wall?

13 ft