The lower base of a trapezoid is 16 cm. If the upper base is extended by 4 cm, it becomes a parallelogram. At this time, the area increases by 20 cm2. What is the area of the original trapezoid in cm2?
一个梯形的下底是16厘米，把上底延长4厘米，就变成平行四边形，这时面积增加20平方厘米，原来的梯形面积是多少平方厘米．
<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<gadget id="calculator">12 + 16</gadget>
<output>28</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">20 * (1/2)</gadget>
<output>10</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">28 * 5</gadget>
<output>140</output>

<result>140</result>