A rectangular cardboard with a length of 30 cm and a width of 20 cm, cut a square with a side length of 5 cm from the four corners, and then fold it into a carton without a lid. What is the outside area of the carton in square centimeters?
一张长30厘米、宽20厘米的长方形硬纸板，从四个角上分别剪去一个边长为5厘米的正方形，然后将它折叠成一个无盖纸盒．该纸盒的外表面积是多少平方厘米？
<gadget id="calculator">30 * 20</gadget>
<output>600</output>

<gadget id="calculator">5 * 5 * 4</gadget>
<output>100</output>

<gadget id="calculator">600 - 100</gadget>
<output>500</output>

<result>500</result>