The scoring rules of football games are: 3 points for a win, 1 point for a tie, 0 points for a loss, 15 games played, 4 losses, and a total of 31 points. How many games has this team won?
足球比赛的记分规则是：胜一场记3分，平一场记1分，负一场记0分，参加15场比赛，负4场，共得31分，则这支球队共胜了几场？
<gadget id="calculator">31 - 15</gadget>
<output>16</output>

<gadget id="calculator">4 + 16</gadget>
<output>20</output>

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

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<result>10</result>