A trapezoid, if only the upper base is extended by 3 cm, becomes a square with a side length of 6 cm, what is the area of the trapezoid in square centimeters?
一个梯形，如果只把上底延长3厘米，就变成了边长6厘米的正方形，这个梯形的面积是多少平方厘米．
<gadget id="calculator">6 - 3</gadget>
<output>3</output>

<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">9 * 3</gadget>
<output>27</output>

<result>27</result>