Additional Algo $5-1$ Demand with Mixed Products

An auto repair shop with three processes $($oil change, tire service, and checkout$)$ has two types of customers $($tires$-$only and full service$).$ An auto repair shop has a demand of $30$ tires$-$only customers per day and $20$ full service customers per day. Tires$-$only customers visit the tire service and checkout processes while full service customers visit all three processes.

What is the total demand at the checkout process each day?

Answer is complete but not entirely correct.

Total demand of customers per day