A right-angled trapezoid has a lower base of 40 meters. If the upper base is increased by 30 meters, the land becomes a square. What is the area of the original trapezoid in square meters?
一块直角梯形地，它的下底40米，如果上底增加30米，这块地就变成了正方形，原梯形的面积是多少平方米．
<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<gadget id="calculator">10 + 40</gadget>
<output>50</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">50 * 20</gadget>
<output>1_000</output>

<result>1_000</result>