For a trapezoid, if the lower base remains unchanged, increase the upper base by 2 cm, and increase the area by 4.8 square centimeters; if the upper base and lower base remain unchanged. Increase the height by 2 centimeters and increase the area by 6.8 square centimeters. Find the area of the original trapezoid?
一个梯形，如果下底不变，将上底增加2厘米，面积增加4.8平方厘米；如果上底和下底不变．将高增加2厘米，面积增加6.8平方厘米，求原来梯形的面积？
<gadget id="calculator">4.8 / 2</gadget>
<output>2.4</output>

<gadget id="calculator">8.5 / 2</gadget>
<output>4.25</output>

<gadget id="calculator">2 * 2.4 * 4.25</gadget>
<output>20.4</output>

<result>20.4</result>