During recess, there are 34 people playing table tennis, some are singles and some are doubles. It is known that there are 12 tables in total. How many people are there in doubles?
课间时，有34人在打乒乓球，有的是单打，有的是双打，已知一共有12张球桌，双打的有多少人？
<gadget id="calculator">12 * 4</gadget>
<output>48</output>

<gadget id="calculator">48 - 34</gadget>
<output>14</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<gadget id="calculator">12 - 7</gadget>
<output>5</output>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<result>20</result>