A trapezoid, if the upper base is increased by 2.5 cm, it becomes a parallelogram; if the upper base is reduced by 4 cm, it becomes a triangle. At this time, the area is reduced by 12 square centimeters from the original trapezoid. What is the area of the original trapezoid in square centimeters? ．
一个梯形，如果上底增加2.5厘米，就变成一个平行四边形；如果上底减少4厘米，就成了一个三角形，这时面积比原梯形减少了12平方厘米，原梯形的面积是多少平方厘米．
<gadget id="calculator">4 + 2.5</gadget>
<output>6.5</output>

<gadget id="calculator">4 + 6.5</gadget>
<output>10.5</output>

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

<gadget id="calculator">12 * (1/2)</gadget>
<output>6</output>

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

<gadget id="calculator">10.5 * 3</gadget>
<output>31.5</output>

<result>31.5</result>