Airline passengers arrive randomly and independently at the passenger-screening

Airline passengers arrive randomly and independently at the passenger-screening facility at a major international airport. The mean arrival rate is 7 passengers per minute 

a.       Compute the probability of no arrivals in a one-minute period (to 6 decimals)

b.      Compute the probability that 3 or fewer passengers arrive in a one-minute period (to 4 decimals)

c.       Compute the probability of no arrivals in a 15 second period (to 4 decimals)

d.      Compute the probability of at least one arrival in a 15-second period (to 4 decimals)