Bill's Barbershop has two barbers available to cut custom$-$ ers' hair. Both barbers provide roughly the same experi$-$ ence and skill, but one is just a little bit slower than the other. The process flow in Figure $5\mathrm{.}9$ shows that all cus$-$ tomers 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 indi$-$ cate the minutes it takes that activity to process a customer. a$.$ How long does it take the average customer to complete this process? b$.$ What single activity is the bottleneck for the entire process? C$.$ How many customers can this process serve in an hour? B$3-$a $(15)$