The school organizes a Go competition. It is known that there are less than 20 players entering the finals. The number of girls is 1/3 of the number of boys, and there is a game between every two players. After all the games are over, there is no draw. And the ratio of the total number of games won by girls to the total number of games won by boys is 4:7. How many boys are there in the finals?
学校组织围棋比赛，已知进入决赛的选手不足20人，其中女生人数是男生人数的(1/3)，且每两个人之间都要进行一场比赛，全部比赛结束后，没有出现平局．并且女生赢得比赛的总场数与男生赢得比赛的总场数之比是4：7．参加决赛的男生一共有多少人？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">12 * (3/4)</gadget>
<output>9</output>

<result>9</result>