Chick$-$fil$-$A is considering the addition of a hand$-$scooped milk shake onto their menu. The milk shake would sell for $$4\mathrm{.}00,$ and would take $30$ seconds to prepare for each customer. Chick$-$fil$-$A has a corporate policy that customers should be served within $1\mathrm{.}5$ minutes. In order to adhere to this policy, they are planning to hire a dedicated milk shake maker to work at the facility. Analysis has revealed that both the time between arriving customers and the time to make a milk shake are distributed exponentially. Given the variability, Chick$-$fil$-$A has determined that the average throughput time for a milk shake must be no more than $50$ seconds in order to consistently meet the $1\mathrm{.}5$ minute service standard. What is the maximum number of customers$/$hour who can order a milkshake and still have the average throughput time within the $50$ second limit$?$