A treasurer wants to measure the overall payment cost for the month. The venture had $4,000 in gross sales and $120 in payment-processing fees. Text exhibit: A simple data card titled Monthly Payment Cost. It shows two large labeled figures: Gross sales $4,000 and Payment-processing fees $120. Under the figures, show a blank line labeled Effective payment fee rate = fees divided by gross sales. Do not show the computed percentage. Which metric is most useful?