trapezoid, if the upper base is increased by 4cm, becomes a parallelogram; if the upper base is decreased by 3cm, it becomes a triangle, and the area is reduced by 7.5cm**2. What is the area of this trapezoid in square centimeters?
一个梯形，如果上底增加4cm，就变成一个平行四边形；如果上底减少3cm，就成了一个三角形，这时面积比原来减少了7.5cm**2．原来这个梯形的面积是多少平方厘来？
<gadget id="calculator">3 + 3 + 4</gadget>
<output>10</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">7.5 * (2/3)</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

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

<result>25</result>