A circular flower pond has a diameter of 80 decimeters. After expansion, the diameter increases to 100 decimeters. How many square meters has the area of the flower pond increased?
一个圆形花池，直径为80分米，扩建后直径增加到100分米，这个花池的面积增加了多少平方米？
<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<gadget id="calculator">50 ** 2</gadget>
<output>2_500</output>

<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<gadget id="calculator">40 ** 2</gadget>
<output>1_600</output>

<gadget id="calculator">2_500 - 1_600</gadget>
<output>900</output>

<gadget id="calculator">900 / 100</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<result>28.26</result>