There is a rectangular swimming pool in the National Fitness Center. The length is 30 meters longer than the width. If the swimming pool is expanded into a smallest square, the area will increase by 2100 square meters. What is the original area of the swimming pool in square meters?
全民健身中心有一个长方形游泳池，长比宽长30米，如果把这个游泳池扩建成一个最小的正方形，面积就增加2100平方米，问原来游泳池的面积是多少平方米．
<gadget id="calculator">2_100 / 30</gadget>
<output>70</output>

<gadget id="calculator">70 - 30</gadget>
<output>40</output>

<gadget id="calculator">70 * 40</gadget>
<output>2_800</output>

<result>2_800</result>