Context: A small cafeteria serves very popular drinks and operates for 8 hours per day, 7 days per week. It charges customers $10 per drink. The data shows that customers arrive at the caf at an average of one every 5 minutes. The caf employs one staff, and, on average, it takes 4 minutes for the staff to serve each customer (from taking the order and the payment as well as making the drink). (Assume a Poisson distribution for the arrival rate of customers and exponential distribution for the service time performed by the staff).

Question: To improve the service, the management wants to reduce the probability of customers waiting outside the caf down to 10%. How would that decision affect the service time and customer's waiting time? Use trial and error to find the answer, and show the two closest figures above and below your final answer at 2 decimal points