There is a rectangular iron sheet with a length of 40 cm and a width of 30 cm. After cutting off squares of equal area at the four corners, it is just folded into an open tin box with a depth of 5 cm. Find the volume of the tin box.
有一块长40厘米，宽30厘米的长方形铁皮，在四个角上分别剪去面积相等的正方形后，正好折成一个深5厘米的无盖铁皮盒，求这个铁皮盒的容积．
<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">5 / 1_000</gadget>
<output>1/200 = around 0.005</output>

<gadget id="calculator">30 * 20 * (1/200)</gadget>
<output>3</output>

<result>3</result>