Cut off the four corners of a piece of cardboard with a length of 30 cm and a width of 15 cm to form a square with a side length of 5 cm, and then fold it into a rectangular box without a cover. Find the volume of the box.
把一块长30厘米、宽15厘米的硬纸板四个角分别剪去边长是5厘米的正方形，然后折成一个无盖的长方体纸盒，求这个纸盒的体积．
<gadget id="calculator">5 * 2</gadget>
<output>10</output>

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

<gadget id="calculator">15 - 10</gadget>
<output>5</output>

<gadget id="calculator">20 * 5 * 5</gadget>
<output>500</output>

<result>500</result>