b$.$ The dean of the college has received a number of complaints from students about the length of time they must wait to have their schedules approved. The dean feels that waiting an average of $7$ minutes to get a schedule approved $($including service$)$ is not unreasonable. Each assistant the dean assigns to the adviser's office will reduce the average time required to approve a schedule by $0\mathrm{.}25$ minute, down to a minimum time of $2\mathrm{.}00$ minute to approve a schedule. How many assistants should the dean assign to the adviser?