Uncle Wang bought back a case of beer, 12 bottles in total, and the shop stipulated that 7 empty bottles could be exchanged for 3 bottles of beer. Calculate how many bottles of beer Uncle Wang can drink at most?
王叔叔买回一箱啤酒，共12瓶，商店规定7个空瓶又可换回3瓶啤酒．算一算王叔叔最多能喝到多少瓶啤酒？
<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">12 + 6 + 3</gadget>
<output>21</output>

<result>21</result>