Find a Doctor is a small startup that helps people find a physician who best meets their needs $($location$,$ insurance accepted, etc.$).$ During a $$slow$$ time for it$,$ it has $8$ staff members taking calls from customers. On average, one call arrives every $7$ minutes $($with a standard deviation of $7$ minutes$).$ Each staff member spends on average $21$ minutes with each customer $($with a standard deviation of $31\mathrm{.}50$ minutes$).$How long does one of their customers spend, on average, waiting on hold before he or she can start speaking to a representative?