It took Fred 12 hours to travel over pack ice from one town in the Arctic to another town 360 miles away. During the return journey, it took him 15 hours. Assume the pack ice was drifting at a constant rate, and that Fred's snowmobile was traveling at a constant speed relative to the pack ice. What was the speed of Fred's snowmobile? 

a. 27 miles per hour 

b. 30 miles per hour  

c. 10 miles per hour

d. 3 miles per hour