During the First 18 Minutes of a 1

Multiple Choice

During the first 18 minutes of a 1.0-hour trip, a car has an average speed of 11 m/s. What must the average speed of the car be during the last 42 minutes of the trip be if the car is to have an average speed of 21 m/s for the entire trip?

A) 21 m/s
B) 23 m/s
C) 25 m/s
D) 27 m/s
E) 29 m/s