A statistics class weighed 20 bags of grapes purchased from the store. The bags are advertised to contain 16 ounces, on average. The class calculated the 90 percent confidence interval for the true mean weight of bags of grapes from this store to be open paren 15 point 8 7 5 comma 16 point 5 9 5 close paren ounces. What is the sample mean weight of grapes, and what is the margin of error?