The army allocates dormitories. If there are 3 people in each room, there will be 20 more people; if there are 6 people in each room, the remaining 2 people can each live in a room. Now each room has 10 people, how many rooms can be vacated?
军队分配宿舍，如果每间住3人，则多出20人；如果每间住6人，余下2人可以每人各住一个房间，现在每间住10人，可以空出多少个房间？
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">12 - 2</gadget>
<output>10</output>

<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<gadget id="calculator">6 - 3</gadget>
<output>3</output>

<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<gadget id="calculator">30 + 20</gadget>
<output>50</output>

<gadget id="calculator">50 / 10</gadget>
<output>5</output>

<gadget id="calculator">10 - 5</gadget>
<output>5</output>

<result>5</result>