Okay so....

A sandbag is dropped from a balloon at a height of 60 meters when the angle of elevation to the sun is 30 degrees. Find the rate at which the shadow of the sandbag is traveling along the ground when the sandbag is at a height of 35 meters.

Position Function: s(t) = 60-4.9t^2

Help would be much appreciated...this one is giving me fits..I think I want to solve this by proportion but I'm really not sure.