The local baseball team conducts a study to find the amount spent on refreshments at the ballpark. Over the course of the season, they gather simple random samples of 500 men and 1000 women. For men, the average expenditure was $20, with a standard deviation of $3. For women, it was $15, with a standard deviation of $2. What is the 99 % confidence interval for the spending difference between men and women? Assume that two populations are independent and normally distributed.