right-angled trapezoid has a lower base of 40 meters. If the upper base is increased by 38 meters, it becomes a square. What is the area of the original trapezoid in square meters?
一个直角梯形，它的下底是40米，如果上底增加38米，它就变成了正方形，原来梯形的面积是多少平方米．
<gadget id="calculator">40 - 38</gadget>
<output>2</output>

<gadget id="calculator">2 + 40</gadget>
<output>42</output>

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

<gadget id="calculator">42 * 20</gadget>
<output>840</output>

<result>840</result>