truck and the steel on it weigh 20 tons. After pouring out half of the steel, the truck weighs 13 tons. How many tons does the truck weigh?
一辆卡车连同车上的钢材重20吨，倒出一半钢材后，连车共重13吨，车重几吨？
<gadget id="calculator">20 - 13</gadget>
<output>7</output>

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

<gadget id="calculator">20 - 14</gadget>
<output>6</output>

<result>6</result>