Q-Mart is interested in comparing customers who use its own charge card with those who use other types of credit cards. Q-Mart would like to know if customers who use the Q-Mart card spend more money per visit, on average, than customers who use some other type of credit cards.

Suppose Q-Mart plans to obtain information on a randomly selected sample of customers using each type of charge card, using equal sample sizes. The estimated common standard deviation is 70.

B)How many customers should be in each sample to achievea 95% confidence interval for the difference between means with approximate half-length of 25? ___________