Bloomington has two hospitals. Hospital $1$ has four ambulances, and hospital $2$ has two ambulances. Ambulance service is deemed adequate if there is only a $10\%$ chance that no ambulance will be available when an ambulance call is received by a hospital. The average length of an ambulance service call is $20$ minutes. Given this information, queueing theory indicates that hospital $1$ can be assigned up to $4\mathrm{.}9$ calls per hour and that hospital $2$ can be assigned up to $5\mathrm{.}5$ calls per hour. Bloomington has been divided into $12$ districts. The average number of calls per hour emanating from each district is given in the file P$05\_71.$xlsx$.$ This file also shows the travel time $($in minutes$)$ needed to get from each district to each hospital. The objective is to minimize the average travel time needed to respond to a call. Determine the proper assignment of districts to hospitals. $($Note: A given district$$s calls do not all have to be assigned to the same hospital.$)$