Airline travelers should be ready to be more flexible as airlines once again cancel thousands of flights this summer. The coalition for Airline Passengers Rights, Health, and Safety averages $400$ calls a day to help stranded travelers deal with airlines. Suppose the hotline is staffed for $16$ hours a day. a$.$ Calculate the average number of calls in a one$-$hour interval, $30-$minute interval, and $15-$minute interval.