Calculus velocity and time question

Question

A car enters an highway at time t = 0 and after 3 hours exits 210 miles away from the entrance junction. You and your two good friends, twins Salt and Pepper, are having a spirited conversation about this.

a. Your friend Salt claims that at some instant during these three hours, the car’s velocity must have been greater than the speed limit of 65 miles per hours. Do you agree with your friend?

b. Your friend Pepper claims that at all times during these three hours, the car’s velocity must have been over the speed limit of 65 miles per hours. Do you agree with your friend?

Answer 1

210/3 =70 mph average speed

a) for at least one instant speed > 65 mph

0 mph for 3 hours & 210 miles per one instant averages to 70 mph

b) but not necessarily all the time

75mph for 1 1/2 hours and 65 mph for the other 1 1/2 hours is a realistic possiblity

or 70 mph all the time, but only with a constant speed