A batch of goods weighing 4 tons has transported 1500 kilograms, how many kilograms are left.
一批重4吨的货物，运走了1500千克，还剩多少千克．
<gadget id="calculator">4 * 1_000</gadget>
<output>4_000</output>

<gadget id="calculator">4_000 - 1_500</gadget>
<output>2_500</output>

<result>2_500</result>