The coffee shop in the business school is open until 9:00 p.m. each week day. The amount of coffee sold after 8:00 p.m. each day is normally distributed with a mean of 15 cups and a standard deviation of 3 cups. At 8:00 p.m., two new pots of coffee are prepared, each containing 10 cups. If demand exceeds supply, more coffee will have to be prepared. What is the probability that they will not have to prepare more coffee?