A piece of right-angled trapezoidal land, its upper base is 40 meters, if the lower base is reduced by 20 meters, it becomes a square. Find the area of the original trapezoid.
一块直角梯形的土地，它的上底是40米，如果下底减少20米，就变成了一个正方形．求原梯形的面积．
<gadget id="calculator">40 + 40 + 20</gadget>
<output>100</output>

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

<gadget id="calculator">100 * 20</gadget>
<output>2_000</output>

<result>2_000</result>