It would be 40 miles per hour. That is because if 20 miles is what he can cover in a half hour, than in one full hour he would go twice the amount of time. So 20 times 2 is fourty. So 40 miles per hour is the answer.
since mike has only been driving for half an hour and drove 20 miles that means that if he goes the same speed for another half hour then his total will be 40 miles in an hour.
