In the basketball game, Zheng Xiong scored 9 2-pointers and 3-pointers and scored 21 points. How many 2-pointers did Zheng Xiong score?
郑雄在篮球比赛中，2分球和3分球一共投进了9个，共获得21分，郑雄投进了多少个2分球．
<gadget id="calculator">3 * 9</gadget>
<output>27</output>

<gadget id="calculator">27 - 21</gadget>
<output>6</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">6 / 1</gadget>
<output>6</output>

<result>6</result>