Answer:
23%
Step-by-step explanation:
Overage cost(Co) = $0.75
Underage cost(Cu) = $2.50
Service level = Cu/(Co + Cu)
Service level = $2.50 / ($0.75+$2.50)
Service level = $2.50 / $3.25
Service level = 0.76923077
Service level = 76.92%
So the optimal service level is 77%
Risk of stock-out = 100% - Service level
Risk of stock-out = 100% - 77%
Risk of stock-out = 23%