For a right-angled trapezoid, if its lower base is shortened by 4 decimeters, the area is reduced by 16 decimeters, and it becomes a square. Find the area of the original trapezoid.
一个直角梯形，将它的下底缩短4分米，面积就减少16分米，且变成了一个正方形．求原来梯形的面积．
<result>42</result>