For a set of opposite sides of a square, one side increases by 16 cm, and the other side decreases by 8 cm, forming a trapezoid. The length of the lower base is three times that of the upper base. Find the area of the trapezoid?
正方形的一组对边，一条边增加16厘米，另一条边减少8厘米，变成一个梯形，下底的长度是上底的3倍，求梯形的面积？
<gadget id="calculator">20 - 8</gadget>
<output>12</output>

<gadget id="calculator">12 + 20 + 16</gadget>
<output>48</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">48 * 10</gadget>
<output>480</output>

<result>480</result>