A local deli chain advertises a "heart healthy" sandwich on the menu. Suppose that the amount of fat grams in a "heart healthy" sandwich is a normal random variable. To estimate the average amount of fat grams in "heart healthy" sandwiches, a nutritionist selects a random sample of four "heart healthy" sandwiches. The sample yielded = 11 grams and s = 1.8 grams. Construct a 90% confidence interval for the average amount of fat grams in a "heart healthy" sandwich.