Please explain why this these are the correct answers to parts A and B

Problem 5-17 (Algo) The diagram describes a service process where customers go through either of two parallel three-step processes and then merge into a single line for two final steps. Capacities of each step are shown on the diagram. a. What is the current capacity of the entire system? b. If you could increase the capacity of only one operation through process improvement efforts, which operation would you select, how much additional capacity would you strive for, and what would the resulting capacity of the process be