If the upper base of a trapezoid is increased by 2 cm, it becomes a square with a side length of 4 cm. What is the area of the trapezoid in square centimeters?
一个梯形，如果上底增加2厘米，就成为一个边长4厘米的正方形，这个梯形的面积是多少平方厘米．
<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">2 + 4</gadget>
<output>6</output>

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

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<result>12</result>