There is a trapezoid, if its upper base and lower base remain unchanged, and its height increases by 2 decimeters, its area increases by 8.5 square decimeters; if its upper base increases by 2 decimeters, its lower base and height remain unchanged, Its area increases by 4.8 square decimeters. What is the area of the original trapezoid?
有一个梯形，如果它的上底和下底都不变，高增加2分米，它的面积就增加8.5平方分米；如果它的上底增加2分米，下底和高都不变，它的面积就增加4.8平方分米．原来梯形的面积是多少？
<gadget id="calculator">4.8 / 2</gadget>
<output>2.4</output>

<gadget id="calculator">8.5 / 2 / 2</gadget>
<output>2.125</output>

<gadget id="calculator">2 * 2.4 * 2 * 2.125</gadget>
<output>20.4</output>

<result>20.4</result>