The operations department will install 4 new copiers. Professors who want to use the copiers arrive at the rate of 70 per hour. The coefficient of variation of the inter-arrival times is 2.

If all of the copiers are busy, the professors will wait until a copier is available.

The average copier usage time for each professor is 145 seconds. The standard deviation of the usage times is only 20 seconds.

On average, how many professors are waiting to use a copier?