The local Food King grocery store has eight possible checkout stations with registers. On Saturday mornings customer traffic is relatively steady from 8 a.m. to noon. The store manager would like to determine how many checkout stations to staff during this time period. The manager knows from information provided by the store's national office that each minute past 3 minutes a customer must wait in line costs the store on average $50 in ill will and lost sales. Alternatively, each additional checkout station the store operates on Saturday morning costs the store $60 in salary and benefits. The following table shows the waiting time for the different staff levels.

Registers staffed	1	2	3	4	5	6	7	8
Waiting time (mins)	20	14	9	4	1.7	1	0.5	0.1

How many registers should the store staff, and why?