The first customer arrived when the shop opened, the next customer arrived $3\mathrm{.}7$ minutes after it opened, and the third customer arrived $7\mathrm{.}9$ minutes after opening. So$,$ the interarrival time between customers $3$ and $2$ is $(7\mathrm{.}9-3\mathrm{.}7)4\mathrm{.}2$ minutes. The service time for each customer is also available. Assuming this is the pattern of arrival and service in your shop, what will be the utilization of your time if you are the only person serving in the shop?