green should credit treasury stock at?

12) Green Company issued 20,000 shares of $5 par common stock. Six months later Green acquired 4,000 shares of its own common stock at $12 per share. Three months later Green sold 1,000 of these shares at $18 per share. If the cost method is used to record treasury stock transactions, to record the sale of the 1,000 treasury shares, Green should credit Treasury Stock at