Construct a 90% confidence interval, using the inequality 

To test the effectiveness of a new drug that is reported to increase the number of hours of sleep patients get during the night, researchers randomly select 13 patients and record the number of hours of sleep each gets with and without the new drug. 

Use the given formula to find the confidence interval. First calculate d, which represents the mean of the differences between the paired data entries, using the formula below, where d represents the difference between entries for a data pair and n = 13 represents the number of pairs of data.