There is a trapezoid, if the upper base is increased by 2 meters, the lower base and height remain the same. Its area increases by 4.8 square meters; if the upper and lower bases remain unchanged, and the height increases by 2 meters, its area increases by 8.5 square meters. Find the area of the original trapezoid.
有一个梯形，如果上底增加2米，下底和高都不变．它的面积就增加4.8平方米；如果上底和下底都不变，高增加2米，它的面积就增加8.5平方米．求原梯形的面积．
<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>