The following are the heat-producing capacities of coal from two mines (in millions of calories per ton): Mine A: 8,500, 8,330, 8,480, 7,960, 8,030 Mine B: 7,710, 7,890, 7,920, 8,270, 7,860 Assuming that the data constitute independent random samples from normal populations with equal variances, construct a 99% confidence interval for the difference between the true average heat-producing capacities of coal from the two mines.