Hi everyone,
I am having a hard time finding my lambda for this homework question. I know something has to be multiplied to get it into the same units and that lambda has to be an average. However all the information I am given is an average. If you could help me that would be great!!

Here is the question:

Suppose you were the manager of a coffee shop with three servers, who each take an average of 1.8 minutes to serve a customer. You have, on average, a customer arriving every 0.8 minutes.

You are considering two options to ensure faster service: a) hiring a fourth sever or b) renting a faster dispensing machine, which would reduce the service time to 1.3 minutes, on average.

You decide to base your decision on the number of customers who arrive during the time you can serve them. You don't want to have more than 10% chance of more customers arriving than you can serve. For instance, with your current operation, you can serve three customers in 1.8 minutes, so you don't want the chance of more than three customers arriving in 1.8 minutes to be greater than 10%.