A nationwide retailer wants to test whether new product shelf facings are effective in increasing sales volume. New shelf facings for the soft drink Country Time are tested at a random sample of 15...

A nationwide retailer wants to test whether new product shelf facings are effective in increasing sales volume. New shelf facings for the soft drink Country Time are tested at a random sample of 15 stores throughout the country. Data on total sales of Country Time for each store, for the week before and the week after the new facings are installed, are given below:

Using the 0.05 level of significance, do you believe that the new shelf facings increase sales of Country Time?