Your store has an average of 40 customers per an eight hour shift. You need to know whether you should hire 1, 2, 3 or 4 salespersons. The waiting times is 15 minutes with one salesperson, 12 minutes with two, 10 minutes with three and 6 minute with a fourth. The cost per a minute that customers wait is $1.00. The cost per a salesperson per an hour is $8.00. How many salespersons should you hire?