A table showing Tickets Sold, Cost, and Total. The first row shows Child, with the entries, c, 3, and 3 c. The second row shows Adult, with entries, x, 5, 5 x. The last row shows Total, with all three entries blank. 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?