Consider a single server queueing system where the customers arrive according to a Poisson process with a mean rate of 18 per hour, and the service time follows an exponential distribution with a mean of 3 minutes. (1). What is the probability that there are more than 3 customers in the system? (2). Compute L, L and L.. (3). Compute W, W, and W. (4). Suppose that the mean arrival rate is 21 instead of 18, what is the new value of L and W? Why?