A system with 2 tellers but only 1 queue line is considered an M/M/1 queue with doubled service rate or M/M/2 queue with original service rate?

For example, this question is solved as M/M/1 or M/M/2? Please explain as soon as possible, thanks in advance.

Example: Bank with 2 tellers. Customers arrive at a rate of 80 per hour and wait in a single line. Average time to serve is 1.2 minutes per customer.

1. What is the expected number of customers present in the bank?

1. What is the expected length of time a customer spends in the bank?

1. What is the fraction of time any specific teller is idle?