There used to be 20 tons of soybeans in the warehouse, but 3 trucks were transported away, each with 4.5 tons. How many tons of soybeans are left in the warehouse?
仓库里原来有20吨大豆，运走了3车，每车4.5吨．仓库里还有多少吨大豆？
<gadget id="calculator">4.5 * 3</gadget>
<output>13.5</output>

<gadget id="calculator">20 - 13.5</gadget>
<output>6.5</output>

<result>6.5</result>