The playground of Xinzhuang Primary School was originally a square. When expanding the campus, the opposite sides of the playground are increased by 18 meters, so the area of the playground is increased by 900 square meters. How many square meters is the original playground area? (Draw a picture on the picture first, then answer)
新庄小学的操场原来是一个正方形．扩建校园时，操场的一组对边各增加18米，这样操场的面积就增加了900平方米，原来操场的面积是多少平方米？(先在图上画一画，再解答)
<gadget id="calculator">900 / 18</gadget>
<output>50</output>

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

<result>2_500</result>