If $\backslash$lambda $=8$ CUSTOMERS$/$HOUR and $\backslash$mu $=10$ CUSTOMERS$/$HOUR$,$ in a single server model, what is the probability that there will be exactly $4$ people in the system?

a$.0\mathrm{.}082$

b$.0\mathrm{.}148$

c$.0\mathrm{.}162$

d$.0\mathrm{.}428$