A tool crib with one attendant serves a group of 10 mechanics.

Mechanics work for an exponentially distributed amount of time with a mean

of 20 minutes, then go to the crib to request a special tool. Service times

by the attendant are exponentially distributed, with a mean of 3 minutes.

If the number of attendants can now be changed and if an attendant is paid

$6 per hour and a mechanic is paid $10 per hour, determine the number of

attendants that should serve in the system in order to minimize the total

cost per hour to the system.

If you could answer this that'd be great!