Problem $6-8$

Safety regulations require that the time between airplane takeoffs $($on the same runway$)$ will be at least $3$ minutes. When taking off, the run time of an airplane on the runway is $45$ seconds. Planes are on average waiting $4$ minutes and $15$ seconds for take$-$off. On average there are $15$ planes taking off per hour. How many planes are either on the runway or waiting to take off? $($Round your answer to $2$ decimal places.$)$

Number of airplanes