Do not miss it with the "solution" by @josgarithmetic, which is presented in TERRIBLE form.
OK, I will copy/paste that my solution here again for your convenience.
The remaining trip is 20 - 5 = 15 miles long.
Mike spends = of an hour = 15 minutes for the first part of the trip;
hence, he spends 30 - 15 = 15 minutes for the remaining part.
Thus Mike moves remaining part of 15 miles in 15 minutes;
hence, his speed is 1 mile per minute, or 60 miles per hour. ANSWER
