The school has a rectangular playground. When it is expanded, its length is increased by 20 meters, or its width is increased by 15 meters, and the area is increased by 600 square meters. What is the original playground area in square meters?
学校有一个长方形操场，扩建时把它的长增加了20米，或宽增加15米，面积都增加600平方米，原来操场的面积是多少平方米？
<gadget id="calculator">600 / 20</gadget>
<output>30</output>

<gadget id="calculator">600 / 15</gadget>
<output>40</output>

<gadget id="calculator">30 * 40</gadget>
<output>1_200</output>

<result>1_200</result>