A boy leaves on a bicycle trip at the rate of 8 mph. One hour later the father, realizing that his son forgot his camping gear, sets out by car. How fast must the father drive to overtake the boy in 15 minutes? 32 mph 36 mph 40 mph

To catch him in 15 minutes the father must travel 32 miles per hour faster (since 1/4 hr * 32 mph = 8 miles)...
Thus the father must drive at 40 miles per hour.