For a trapezoid, if the upper base is extended by 5 cm, the area increases by 25 cm2 and becomes a parallelogram. Given that the lower base of the original trapezoid is 7 cm, find the area of the original trapezoid.
一个梯形，若上底延长5厘米，面积就增加25平方厘米，并且变成了一个平行四边形．已知原梯形的下底是7厘米，求原梯形的面积．
<gadget id="calculator">7 - 5</gadget>
<output>2</output>

<gadget id="calculator">2 + 7</gadget>
<output>9</output>

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

<gadget id="calculator">25 * (2/5)</gadget>
<output>10</output>

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

<gadget id="calculator">9 * 5</gadget>
<output>45</output>

<result>45</result>