Tickets to a baseball game cost $3 for a child’s ticket and $5 for an adult ticket. At the last game, $521 was collected when 139 people attended the game. Which value could replace x in the table so that a single-variable equation can be written and solved to determine the number of child’s tickets, c, sold?

Let c represent the number of children’s tickets. Since 139 people attended altogether, the number of adult tickets is 139 − c, so x should be 139 − c. Then the money collected can be represented by 3c + 5(139 − c) = 521, a single-variable equation. Thus, 139 − c is the correct choice.

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