A small parking lot has 3 spaces (bays). Vehicles arrive randomly (according to a Poisson process) at an average rate of 6 vehicles per hour. The parking time has an exponential distribution with a mean of 30 minutes. If a vehicle arrives when the three spaces are occupied, it leaves immediately without waiting or returning.
a) Find the percentage of lost customers, i.e., vehicles that arrive but cannot park due to full occupancy.
b) Find the average number of vehicles in the parking lot.
c) To reduce the percentage of lost customers, the parking lot manager has added a "waiting zone" near the entrance, where at most one vehicle can wait for a vacant parking space. Find the effect of this arrangement on the percentage of lost customers (assume that vehicles are always willing to use the waiting zone).