To Train for the Running of a Triathlon, Jerri Jogs

Multiple Choice

To train for the running of a triathlon, Jerri jogs 1 hour each day over the same 8-mile course. Six miles of the course is downhill, whereas the other 2 miles is on level ground. Jerri figures that she runs 3 miles per hour faster downhill than she runs on level ground. Find the rate at which Jerri runs on level ground.

A) 7 mph
B) 21 mph
C) 6 mph
D) 18 mph
E) 5 mph