Can anyone provide an explanation for this problem?

For a study conducted by the research department of a pharmaceutical company, 295 randomly selected individuals were asked to report the amount of money they spend annually on prescription allergy relief medication. The sample mean was found to be $17.60 with a standard deviation of $5.50. A random sample of 215 individuals was selected independently of the rst sample. These individuals reported their annual spending on non-prescription allergy relief medication. The mean of the second sample was found to be $13.40 with a standard deviation of $4.40. As the sample sizes were quite large, it was assumed that the respective population standard deviations of the spending for prescription and non-prescription allergy relief medication could be estimated as the respective sample standard deviation values given above. Construct a 95% condence interval for the difference [11 [12 between the mean spending on prescription allergy relief medication ([11] and the mean spending on non-prescription allergy relief medication (LI-2). Then nd the lower limit and upper limit of the 95% condence interval. Carry your intermediate computations to at least three decimal places. Round your answers to at least two decimal places. (If necessary, consult a list of formulas.) Lower limit: Upper limit