There is a fault with the cruise control on Hank's car such that the speed continuously and linearly increases with time.
When he starts off the speed is set to exactly 60 mph. He is driving on a long straight route with the radio on at full blast and he is not paying any attention to his speed. After 3 hours he notices that his speed has now reached 80 mph.
For how many miles did he drive above the state speed limit of 70 mph?
Author: Leslie Green