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; $15-$minute interval. $($Round your answers to $2$