There is a rectangle, its length is removed by 4 centimeters, the area is reduced by 20 square centimeters, the remaining part is exactly a square, what is its area?
有一个长方形，它的长去掉4厘米，面积就减少20平方厘米，剩下的部分正好是一个正方形，它的面积是多少．
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<gadget id="calculator">25 + 20</gadget>
<output>45</output>

<result>45</result>