On Monday mornings, a CIBC branch has only one teller window open for deposits and withdrawals. Experience has shown that the average number of arriving customers in a 4-minute interval on Monday mornings is 2.8, and each teller can serve more than that number efficiently. The random arrivals at this bank on Monday mornings are Poisson distributed.

1. What is the probability that on a Monday morning no one will arrive at the bank to make a deposit or withdrawal during a 4-minute interval? 0.0615

2. Suppose the teller can serve no more than four customers in any 4-minute interval at this window on a Monday morning.

(a) What is the probability that, during any given 4-minute interval, the teller will be unable to meet the demand?

(b) When demand cannot be met during any given interval, a second window is opened. What percentage of the time will a second window have to be opened?

I solve the first one but I'm having trouble with the others one