Mr. Lopez has a choice of two routes to get to work. Route A is 6 miles long, and his average speed along this route is 30 miles per hour. Route B is 5 miles long, and his average speed along this route is 40 miles per hour, except for a 21-mile stretch in a school zone where his average speed is 20 miles per hour. By how many minutes is Route B quicker than Route A? <spanclass=′latex−bold′>(A)</span>243<spanclass=′latex−bold′>(B)</span>343<spanclass=′latex−bold′>(C)</span>421<spanclass=′latex−bold′>(D)</span>521<spanclass=′latex−bold′>(E)</span>643