please help with part c!

The Victoria Theater shows vintage movies. Customers arrive at the theater line at the rate of 100 per hour. The ticket window seller averages 30 seconds per customer, which includes placing validation stamps on customers' parking lot receipts and punching their frequent watcher cards. (Unfortunately, because of these added services, many customers don't get in until after the feature has started.) Use Exhibit 7.13. a. What is the average customer time at the Victoria Theator? Average customer time minutes b. What would be the effect on customer time in the system of having a second ticket taker doing nothing but validations and card punching, thereby cutting the average service time to 20 seconds? (Hint- this is the same model as part a with a shortened service time) (Round your answer to 3 decimal places.) Average time in system minutes c. What would be the customer time in the system if a second window was opened with each server doing all three tasks? (Hint - this a different service model) (Use closest A/ value from Exhibit 7.13. Do not round intermediate calculations. Round your answer to 3 decimal places.) Average time in system minutes