There are 10 football teams in a single round robin match. Each team plays exactly one game against the other teams. The winner gets 3 points, the loser gets 0 points, and the draw gets 1 point for both teams. After the game, the total points of all teams is 120 points, so how many games are tied in the game?
有10支足球队进行单循环赛，每个队都恰好与其他队各比赛一场，胜者得3分，负者得0分，平局两队各的1分．比赛结束后，全部球队的总积分是120分，那么比赛中平局的场数共有多少场．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">3 * 10 * (9/2)</gadget>
<output>135</output>

<gadget id="calculator">135 - 120</gadget>
<output>15</output>

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

<gadget id="calculator">15 / 1</gadget>
<output>15</output>

<result>15</result>