The cost, c, of a ham sandwich at a deli varies directly with the number of sandwiches, n. If c = $54 when n is 9, what is the cost of the sandwiches when n is 3?

Direct variation means the cost per sandwich stays constant. At 9 sandwiches, the cost is $54, so each sandwich costs $54 ÷ 9 = $6. For 3 sandwiches, the cost is 3 × $6 = $18, so the correct choice is $18.

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