The number of people arriving at a fast food drive-thru in any given 2 minute interval obeys a Poisson process with mean 1. Suppose that the waiters can only process 3 orders in any given 4 minute interval (also, assume the waiters can process an order instantaneously, but are limited in how many they can process in given time intervals, as indicated). What is the expected number of people that leave the drive-thru with their orders filled in any given 4 minute interval?