The manager of a restaurant plans to survey a random sample of customers to estimate the proportion of customers who would return within a week if given a coupon for a free dessert to use on their next visit. A similar coupon was given last year, and 30 percent of the customers who were given the coupon returned within a week. The manager will use the observed proportion from last year as a preliminary estimate of the population proportion and wants the margin of error to be at most 0.4 at a 90 percent level of confidence.Of the following, which is the least number of customers who should be surveyed such that the estimate of the margin of error of the 90 percent confidence interval will be no greater than 0.4?