13 sellers and 13 buyers are each willing to buy or sell one unit of a good, with values {$13, $12, $11, $10, $9, $8, $7, $6, $5, $4, $3, $2, $1}. If the market is competitive but the cost of market-making is $4 per transaction, the equilibrium quantity traded in the market is 4. 7 9. 5