A store brings in 20 boxes of towels, 80 in each box, sells 850, how many are left.
一个商店运进毛巾20箱，每箱80条，卖出850条，还剩多少条．
<gadget id="calculator">20 * 80</gadget>
<output>1_600</output>

<gadget id="calculator">1_600 - 850</gadget>
<output>750</output>

<result>750</result>