For a trapezoid, if the upper base is extended by 3 cm, the area increases by 6 cm**2 and becomes a parallelogram. If the upper base of the original trapezoid is 3 cm, what is the area of the original trapezoid in cm2?
一个梯形，若上底延长3cm，面积就增加了6cm**2，且变成了一个平行四边形，如果原梯形的上底是3cm，那么原梯形的面积是多少cm2．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<result>18</result>