The question goes like this:

A highway patrol plane flies 3 miles above a level, straight road at a steead 120 miles per hour. The pilot sees an oncoming car and with radar determines that at the instant the line of sight distance from plane to car is 5 miles, the line of sight distance is decreasing at the rate of 160 miles per hour. Find the speed of the car along the highway.

I am stucked at forming the equations. Please help thanks