Bill's Barbershop has two barbers available to cut$$ customer's hair. Both barbers provide roughly the same experience and$$ skill, but one is just a little bit slower than the other. The process flow below shows that all customers go through steps B$1$ and B$2$ and then can be served at either of the two barbers at step B$3.$ The process ends for all customers at step B$4.$ The numbers in parentheses indicate the minutes it takes that activity to process a customer.

B$1$B$2$B$4$B$3-$aB$3-$b$(8)(10)(15)(10)(9)$

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In the diagram, there are $5$ circles labeled inside each circle using labels B$1,$ B$2,$ B$3-$a$,$ B$3-$b$,$ and B$4.$ There is a number inside parentheses below each label. Also, there are arrows that show the flow through the circles from B$1$ to B$4$ as follows: Circle B$1(8)$ connects to circle B$2(10),$ circle B$2(10)$ connects to circle B$3-$a $(15)$ and to circle B$3-$b $(10),$ and circles B$3-$a $(15)$ and B$3-$b $(10)$ connect to circle B$4(9).$

Part $2$

a$.$ How long does it take the average customer to complete this$$ process?

enter your response here

minutes. $($Enter your response rounded to one decimal$$ place.$)$

Part $3$

b$.$ What single activity is the bottleneck for the entire$$ process?$$

Benter your response here

Part $4$

c$.$ How many customers can this process serve in an$$ hour?

enter your response here

customers per hour. $($Enter your response as an$$ integer.$)$