Question 177599
An indirect proof . . . 
We assume the opposite and prove a contradiction.

Assume that John did NOT exceed the speed limit.

He drove 60 miles at 55 mph.
   This would take him:  60/55  =  1 hour 4½ minutes.

But he drove from 8:15 to 9:00 ... only 45 minutes.

Therefore, he must have driven faster than 55 mph