and B stand face to face with a distance of 30 meters. They play "rock-paper-scissors". The winner moves forward 8 meters, the loser moves back 5 meters, and the draw moves forward 1 meter each. After playing 10 rounds, The distance between the two is 7 meters, so how many rounds are they tied?
甲乙二人相距30米面对面站好，两人玩"石头剪子布"，胜者向前走8米，负者向后退5米，平局两人各向前走1米，玩了10局后，两人相距7米，那么两人平了多少局．
<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">30 - 20 - 7</gadget>
<output>3</output>

<gadget id="calculator">8 - 5 - 2</gadget>
<output>1</output>

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

<gadget id="calculator">30 - 20 - 3</gadget>
<output>7</output>

<result>7</result>