You have a list of 15 items that typical families routinely buy every week when grocery shopping. You looked up the prices of each item on both Amazon's and Walmart's websites. You found the average price per item at Amazon was $8.50 with a standard deviation of $1.50 and the average price per item at Walmart was $9.75 with a standard deviation of $2.00. You would like to know if Walmart is more expensive for staple grocery items than Amazon. Which test should you run?