Cut out a square as large as possible from a rectangular piece of paper with a length of 55 cm and a width of 40 cm. What is the remaining area in square centimeters?
从长55厘米，宽40厘米的长方形纸上，剪下一个尽可能大的正方形，余下的面积是多少平方厘米？
<gadget id="calculator">55 - 40</gadget>
<output>15</output>

<gadget id="calculator">40 * 15</gadget>
<output>600</output>

<result>600</result>