A delivery driver made 3 deliveries this morning. Each delivery route was 10 miles long. For the first delivery, he drove at a speed of 40 miles per hour. For the second, he drove at 25 miles per hour, and for the third, he drove at 50 miles per hour. If the driver had always driven at 40 miles per hour, he would have spent less time on deliveries. How many minutes less?
4
6
8
10
12
