The upper base of a right-angled trapezoid is 12 decimeters. If the upper base is extended by 4 decimeters, it becomes a square. What is the area of the trapezoid?
一个直角梯形的上底是12分米，如果把上底延长4分米，就是一个正方形，这个梯形的面积是多少．
<gadget id="calculator">12 + 4</gadget>
<output>16</output>

<gadget id="calculator">12 + 16</gadget>
<output>28</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">28 * 8</gadget>
<output>224</output>

<result>224</result>