On average, how busy is the server, $?$

a$.0\mathrm{.}6$

b$.0\mathrm{.}75$

c$.0\mathrm{.}9$

d$.0\mathrm{.}8$

Calculate the probability of the server being idle.

a$.0\mathrm{.}25$

b$.0\mathrm{.}1$

c$.0\mathrm{.}4$

d$.0\mathrm{.}2$