The average transaction at a single channel, single phase automatic teller can be completed in $7\mathrm{.}5$ minutes and customers arrive at the average rate of one every ten minutes. On average, what is the server utilization? $($Choose the closest answer.$)$

a$.0\mathrm{.}167$

b$.0\mathrm{.}75$

c$.0\mathrm{.}125$

d$.1\mathrm{.}33$