A Bus Driver Follows a Morning Route and an Afternoon

Multiple Choice

A bus driver follows a morning route and an afternoon route each day. Because there are more cities on the morning route, the average speed is 12 miles per hour less than the afternoon route.
She covers 70 miles on the morning route in the same amount of time as she covers 100 miles on the Afternoon route. Find her average speed on the afternoon route.

A) 51 miles per hour
B) 40 miles per hour
C) 36 miles per hour
D) 28 miles per hour