A piece of rectangular colored paper with a length of 40 cm and a width of 15 cm, cut out the largest square, what is the shape of the remaining part? What is the area of the remaining part?
一张长40厘米、宽15厘米的长方形彩纸，剪去一个最大的正方形，剩下的部分是什么图形？剩下部分的面积是多少？
<gadget id="calculator">40 - 15</gadget>
<output>25</output>

<gadget id="calculator">25 * 15</gadget>
<output>375</output>

<result>375</result>