A sample of 400 orders for take-out food at a local pizzeria found that the average cost of an order was $25 with s=$18.

(a) Find the margin of error, if we use a 95% confidence interval, for the average cost of an order.

(b) Interpret for management the margin of error.

(c) If we need to be 99% confident, does the confidence interval become wider or narrower?

(d) Find the 99% confidence interval.