The Department of Transportation (D. O.T.) in a very large city has organized a new system of bus transportation. In an advertising campaign, citizens are encouraged to use the new "GO-D. O.T!" system. Suppose that at one of the bus stops the length of time (in minutes) that a commuter must wait for a bus is a uniformly distributed random variable, T. The possible values of T are from 0 minutes to 20 minutes. What is the probability that a randomly selected commuter will spend more than 7 minutes waiting for GO-D. O.T?