current_time to 0 and total_waiting_time to 0.current_time, update current_time to the customer's arrival time.
b. Add the customer's preparation time to current_time to get the finish time for this customer's order.
c. Calculate the waiting time for the customer as current_time minus the customer's arrival time.
d. Add the waiting time to total_waiting_time.total_waiting_time by the number of customers.