A bank manager is considering what service design to employ for the teller department. On a typical workday an average of $30$ customers per hour arrive at the bank to see a teller, arriving according to a Poisson distribution. The average time required to transact business is $4$ minutes per customer following an exponential distribution. Currently, the bank has one line for each of its $3$ tellers. However, the manager has computed that if the design was changed to one line that is serviced by all $3$ of the tellers, the average number of people waiting in line would be $0\mathrm{.}89$ customers.

$$ How would the average customer wait$-$time in line be affected by changing the service design?