3. At a post office, customers arrive at an average rate of 18 customers per hour following a Poisson distribution. The store currently has one clerk who can service an average rate of 20 customers per hour (assume Exponential distribution). If the manger is considering adding an extra attendant to improve the system performance. If a clerk is paid $30 per hour while customer waiting is estimated at $20, would it be more cost effective to have one or two clerks at the office