Use a piece of rectangular paper with a length of 10 decimeters and a width of 7 decimeters to cut out the largest square. The area of this square is larger than the area of the remaining figure by how many square centimeters.
用一张长10分米宽7分米的长方形纸，剪出一个最大的正方形，这个正方形的面积比剩下的图形的面积大多少平方厘米．
<gadget id="calculator">7 * 7</gadget>
<output>49</output>

<gadget id="calculator">10 * 7</gadget>
<output>70</output>

<gadget id="calculator">70 - 49</gadget>
<output>21</output>

<gadget id="calculator">49 - 21</gadget>
<output>28</output>

<result>28</result>