A square iron sheet with an area of 900 square centimeters, cut off four small squares of equal area from its four corners, and weld them into a square iron sheet box without a cover (the seams are not noted). What is the surface area of the tin box in square centimeters?
一块正方形铁皮，面积为900平方厘米，在它的四个角剪去四个面积相等的小正方形，焊接成一个无盖的正方体铁皮盒(接缝处不记)．这个铁皮盒表面积是多少平方厘米？
<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 * 10 * 5</gadget>
<output>500</output>

<result>500</result>