$5.$ Consider an espresso stand with a single barista. Customers arrive to the stand at the rate of $28$ per hour on average. The corresponding coefficient of variation of $1($CV $1)$ Service times are exponentially distributed $($i$.$e$.$ the corresponding coefficient of variation of $1)$ with a service rate of $35$ customers per hour. The manager would like to add few more baristas to decrease the total flow time of a customer in the system $($waiting $+$ service$)$ below $2$ minutes $(0\mathrm{.}03333$ hrs$).$ What is the minimum number of baristas $($in total$)$ that will ensure the service goal of less than $2$ minutes, on average?

Select one:

a$.4$

b$.2$ Chat

c$.3$ other

d$.1$