For a right-angled trapezoid, its lower base is shortened by 4 meters, and its area is immediately reduced by 16 square meters, and it becomes a square. Find the area of the original trapezoid.
一个直角梯形，它的下底缩短4米，面积立即就减少了16平方米，而且变成了一个正方形，求原梯形面积．
<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">16 * (1/2)</gadget>
<output>8</output>

<gadget id="calculator">8 + 4 + 8</gadget>
<output>20</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<result>80</result>