A trapezoid, if the upper base is extended by 5 cm, becomes a parallelogram, and the area increases by 15 cm2. If the upper base is 5 cm, what is the area of the original trapezoid?
一个梯形，如果上底延长5厘米，就变成一个平行四边形，且面积增加15平方厘米，如果上底是5厘米，原梯形的面积是多少平方厘米．
<gadget id="calculator">5 + 5</gadget>
<output>10</output>

<gadget id="calculator">5 + 10</gadget>
<output>15</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">15 * (2/5)</gadget>
<output>6</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<result>45</result>