Katie,
Once the skydiver reaches terminal velocity, then he will be falling with constant speed. The distance he falls in time t will then be d = (160 ft/s)·t. And his altitude above the ground (height h) will be his altitude when the parachute opened minus the distance he has fallen so we can write:
h = (3200 ft) - (160 ft/s)·t
As a point of interest, the time it will take him to fall all the way to the ground is t = (3200 ft)/(160 ft/s) = 20 s