The average length of the upper and lower bases of a trapezoid is 12cm, which is exactly twice the height. What is the area of the trapezoid in cm**2.
一个梯形上、下底的平均长度是12cm，正好是高的2倍，这个梯形的面积是多少cm**2．
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

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

<gadget id="calculator">12 * 2 * 3</gadget>
<output>72</output>

<result>72</result>