A 540-mile trip was driven in two legs. The first leg had an average speed of 65 mph, and the remainder was driven at 50 mph. For how long was the car driven at each speed
a) 5 hours at 65 mph, 5 hours at 50 mph
b) 6 hours at 65 mph, 4 hours at 50 mph
c) 7 hours at 65 mph, 3 hours at 50 mph
d) 8 hours at 65 mph, 2 hours at 50 mph