A right-angled trapezoid, if the upper base is increased by 3 cm, becomes a square with a side length of 12 cm. What is the area of the original trapezoid?
一个直角梯形，如果上底增加3厘米，就变成边长12厘米的正方形，原来梯形的面积是多少？
<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<gadget id="calculator">9 + 12</gadget>
<output>21</output>

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

<gadget id="calculator">21 * 6</gadget>
<output>126</output>

<result>126</result>