A moving shadow

Hey guys, I could really use some help. I've been trying to figure this problem out for the past 45 minutes, and I'm getting nowhere.

The problem reads; A light shines from the top of a pole 50 ft high. A ball is dropped from the same height from a point 30 ft away from the light. How fast is the shadow of the ball moving along the ground 1/2 second later? (Assume the ball falls a distance s = 16t^2 in t sec.)

Then we have a picture of a light 50 ft high, with a line from the bottom to point x(t). This forms a right triangle by making a line from the top of the light (50 ft) to point x(t). There is a mark at 30 ft on the ground, and they have the ball on the hypotenuse at that point (where t = 1/2 sec).

I honestly don't know where to start other than finding ds/dt = 32t. Can any of you guys help? Thanks in advance!