the manager of a local recreational center wanted to determine the average amount each consumer spent on traveling to and from the center. on the basis of the findings, the manager was planning on setting the entrance fee. the management noted that customers living at the other side of town had to travel about 15 miles and spent about 20 cents per mile. the manager wanted to be 95% confident of the findings and did not want the margin of error to exceed /- 10 cents. what sample size should the manger use to determine the average travel expenditure