Zhang Hong uses a rectangular piece of paper to draw the surface development of a cube with a side length of 3 cm. What is the minimum area of the rectangular piece of paper?
张红用一张长方形的纸片，画一个棱长3厘米的正方体的表面展开图，长方形纸片的面积最小是多少．
<gadget id="calculator">9 * 6</gadget>
<output>54</output>

<result>54</result>