Solution and Explanation:
Olivia
Average arrival rate, λ = 2.1 problems per hour
Average service rate, μ = 2.9 problems per hour
Assume Poisson arrival and exponential service time in order to make use of the M/M/1 queue formula.
The average number of computes not available (i.e. either waiting for repair or getting repaired), Ls = λ / (μ - λ) = 2.1 / (2.9 - 2.1) = 2.625
Total cost per hour = Ls multiply $17 + $20 = 2.625 multiply 17 + 20 = $64.625
Layla
Average arrival rate, λ = 2.1 problems per hour
Average service rate, μ = 3.6 problems per hour
Ls = λ / (μ - λ) =

Total cost per hour = Ls multiply $17 + $29 = 1.40 multiply 17 + 29 = $52.8
So,
cost saved per hour = 64.625 minus 52.8 = $11.825