Many airlines allow overbooking, as they know that, in practice, not all customers who have made reservations for a flight will show up. AirWise, a small private airline company has planes that only hold 15 people. Past records show that 20% of people making reservations for this company do not show up. Management at AirWise has decided to book 18 people for each flight. Find the probability that:

a) On any given flight, at least one passenger holding a reservation will not have a seat.

b) There will be one or more empty seats on any given flight.