How can i solve this question please

2) Assume that the time between arrivals of customers at a certain grocery store is exponentially distributed and that these times are independent of one another. It is known that, on average, 5 customers arrive every 2 hours. Suppose that we start monitoring arrivals at the store at a particular instant in time. a) [3] From when you start looking, what is the probability that the next customer will arrive within the next 20 minutes? b) [3] What is the probability that exactly two customers will arrive in the next 4 hours? c) [4] What is the probability that the third customer to arrive will do so after 5 hours