4 truckloads of cement are shipped to the construction site, each truckload contains 150 bags, and 320 bags are used. How many bags are left?
工地运来4车水泥，每车150袋，用去320袋，还剩多少袋？
<gadget id="calculator">150 * 4</gadget>
<output>600</output>

<gadget id="calculator">600 - 320</gadget>
<output>280</output>

<result>280</result>