A piece of right-angled trapezoidal cultivated land has a lower base of 30 meters. If the upper base is increased by 6 meters, the land becomes a square. What is the original area of the land in square meters?
一块直角梯形的耕地，它的下底是30米，如果上底增加6米，这块地就变成了正方形，那么原来这块地面积是多少平方米？
<gadget id="calculator">30 - 6</gadget>
<output>24</output>

<gadget id="calculator">24 + 30</gadget>
<output>54</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">54 * 15</gadget>
<output>810</output>

<result>810</result>