Im stuck and need help please. Can some please solve it correctly and quickly. Thank you and God bless.

A bank has two tellers to serve walk-in customers at their branch. Each teller has a separate queue and for each queue, customers arrive at the rate of one customer every 15min. The new bank manager (who took BCOR 3050) wants to pool the two separate queues into one single queue to reduce wait times for customers. Q13. What is the average inter-arrival time for the single pooled queue?. 30min 7.5 15min 10min