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

a$.1\mathrm{.}50$

b$.0\mathrm{.}67$

c$.0\mathrm{.}75$

d$.0\mathrm{.}50$