From 6am to 9am customers arrive in droves to Betty’s Bakery for her annual, 1 day only, cake sale. During that 3 hour period 1.75 customers enters the Bakery every minute. Betty and her staff can box cakes and check out customers only at the rate of 70 customers per hour. What is the average waiting time (minutes) for the customers who arrive in this 3-hour period of time?