The factory shipped a batch of coal. After burning 28 tons, there are 13 tons left. How many tons are there in this batch of coal? (answer in two minutes)
工厂运来一批煤．烧了28吨，还剩13吨，这批煤有多少吨？(用两钟方法解答)
<gadget id="calculator">28 + 13</gadget>
<output>41</output>

<result>41</result>