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, Wang Ming made a total of 9 shots (no free throws) and scored 20 points. How many 2-pointers did he make?
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，王明总共投中9个球(没有罚球)，得了20分，他投中多少个2分球．
<gadget id="calculator">20 - 18</gadget>
<output>2</output>

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

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

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

<result>7</result>