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This is queueing theory problem

An Airport has a single runway and one air traffic controller to land planes. It takes an airplane 12 mins to land and clear the run way. Planes arrive at the Airport at the rate of 4/hour. Determine the average number of planes that will stack up waiting to land. Find the average time a plane must wait in line before it can land. Calculate the average time it takes a plane to clear the runway once it has notified the airport that it is in the vicinity and wants to land. The airport has a rule that an air traffic controller can on the average land planes a maximum of 45 minutes out of every hour. There must be 15 mins of idle time available to relieve the tension. Will this airport needs to hire an extra air traffic controller