The US Federal Aviation Administration (FAA) safety regulations require that the time between airplane takeoffs (on the same runway) will be at least 3 minutes. When a plane is taking off, the fun time of an airplane on the runway is 45 seconds. Planes are on average walting 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