There is a rectangular iron sheet with a length of 40 cm and a width of 30 cm. Cut a square with a side length of 5 cm from each of its four corners to make a rectangular iron box without a lid. Find the volume of the iron box. (The thickness of the iron sheet is ignored)
有一个长方形铁皮，长40厘米，宽30厘米，在它的四角各剪去一个边长为5厘米的正方形，做成一个无盖的长方形铁盒，求这个铁盒的容积．(铁皮的厚度忽略不计)
<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">40 - 10</gadget>
<output>30</output>

<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<gadget id="calculator">30 * 20 * 5</gadget>
<output>3_000</output>

<result>3_000</result>