We need to buy a lot, so we would go to wholesale supermarket to buy our groceries. The closest wholesale place is BJ's Wholesale Club, which is 12 miles away. Ms. Lam drives you and your classmates to BJ's Wholesale Club. On the way back, due to traffics, she drives 6 miles per hour slower, resulting in the return trip taking 4 minutes longer. How fast did she drive on the way to the BJ's Wholesale Club? (be careful, change the time from minutes to hours)