The lower base of a long trapezoid is 7cm, the height is 5cm, and the upper base is extended by 3cm to form a parallelogram. What is the area of the original trapezoid in cm**2.
一个长梯形的下底为7cm，高5cm，上底延长3cm后就形成一个平行四边形，原来的梯形面积为多少cm**2．
<gadget id="calculator">7 - 3</gadget>
<output>4</output>

<gadget id="calculator">4 + 7</gadget>
<output>11</output>

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

<gadget id="calculator">11 * (5/2)</gadget>
<output>55/2 = around 27.5</output>

<result>55/2 = around 27.5</result>