In basketball, a shot outside the 3-point line is worth 3 points, and a shot inside the 3-point line is worth 2 points. In a game, Mr. Lin hit 9 balls and scored 20 points. How many 3-pointers did he hit?
篮球比赛中，3分线外投中一球得3分，3分线内投中一球得2分．在一场比赛中，林老师总共投中9个球，得了20分，他投中了多少个3分球．
<gadget id="calculator">3 * 9</gadget>
<output>27</output>

<gadget id="calculator">27 - 20</gadget>
<output>7</output>

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

<gadget id="calculator">7 / 1</gadget>
<output>7</output>

<gadget id="calculator">9 - 7</gadget>
<output>2</output>

<result>2</result>