How does Lucas find the lambda and Mu for this problem? Not sure how he gets 5 and 8 for arrival rate and 20 and 16 for their service rate for the junior and senior attendant respectively.

Is there someone else who would be able to rework this problem? Doesn't seem quite there.

"The supervisor at the Precision Machine Shop wants to determine the staffing policy that minimizes total operating costs. The average arrival rate at the tool crib, where tools are dispensed to the workers, is eight machinists per hour. Each machinists pay is $20 per hour. The supervisor can staff the crib either with a junior attendant who is paid $5 per hour and can process 10 arrivals per hour or with a senior attendant who is paid $12 per hour and can process 16 arrivals per hour. Which attendant should be selected, and what would be the total estimated hourly cost?"

This is the original question