Cut off the largest triangle from a trapezoid whose upper base is 6 cm, lower base is 9 cm, and height is 4 cm. What is the area of the remaining part in square centimeters?
在一个上底是6厘米，下底是9厘米，高是4厘米的梯形中剪去一个最大的三角形，剩下部分的面积是多少平方厘米．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<result>12</result>