On her way home from work, Brenda drove 20 miles at 60 miles per hour. Due to poor weather conditions, she then reduced her speed to 30 miles per hour for the remainder of the trip. Her entire commute to work is 80 miles in distance. Based on the information provided above, which numerical value best represents how much less time would it have taken Brenda had she driven the entire distance at 40 miles per hour?

A. 1/12 hour
B. 1/6 hour
C. 1/4 hour
D. 1/3 hour
E. 2/3 hour