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$3-$a

B$3-$b

$(9)$

$(7)$

$(12)$

$(10)$

$(15)$

x y graph

Part $2$

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

$$

$55$ minutes. $($