Improperly filled orders are a costly problem for mail- order houses. To estimate the mean loss per incorrectly filled order, a large firm plans to sample n incorrectly filled orders and to determine the added cost associated with each one. The firm estimates that the added cost is between $ 40 and $ 400. How many incorrectly filled orders must be sampled to estimate the mean additional cost using a 95% confidence interval of width $ 20?