need answer asap, will give thumbs up

At a bus stop, there is usually a line of passengers waiting for buses. The number of passengers there varies in time, but eventually they all leave in a bus. On average, there are 5 passengers at the bus stop. On average, a passenger arrives at the stop every 4 minutes. What is the average time a passenger has to wait until s/he departs in a bus? Provide your answer in minutes. Note: If your answer is not an integer, round to the nearest integer