Could someone explain the calculations that go into calculating the gross margin method in the attached example where the answer is 40% I've tried to get the same number with no luck.

The textbook states that it is calcualted as (sales-cost of sales) / sales. but no matter what numbers im using im just not getting 40%

thank you!

GROSS MARGIN METHOD Estimated Results Known Data $10,000 $10,000 Net sales revenue (base amount) Cost of goods sold: Beginning inventory $5,000 $5,000 Add: Purchases 8,000 8,000 Goods available for sale 13,000 (1) 13,000 Less: Ending inventory 7.000 (4) Cost of sales Gross margin "Computational steps: (1) Gross margin rate (estimated as percent of sales based on last year's results) = 40% Goods available for sale, above: $13,000 (2) Gross margin: $4,000 (i.e., $10,000 x 40%) (3) Cost of sales: $6,000 ($10,000 - $4,000) 6,000 (3) $ 4,000 (12)