A driver involved in an accident claims he was going only 25 mph. when police tested his car, they found that when its brakes were applied at 25 mph, the car skidded only 45 feet before coming to a stop. But the driver's skid marks at the accident scene measured 210 feet. Assuming the same (constant) deceleration, determine the speed he was actually traveling just prior to the accident.

This is a physics proplem from my diff eq book, so I'm not supposed to use any formulas I learned in physics.