The bottom is a square cuboid carton, and its sides are unfolded to get a square with a side length of 20 cm. How much cardboard is needed to make this carton?
底面是正方形的长方体纸箱，它的侧面展开正好得到一个边长是20厘米的正方形，做这只纸箱需用多少纸板？
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 5 * 2</gadget>
<output>50</output>

<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">50 + 100</gadget>
<output>150</output>

<result>150</result>