Take the largest rectangle from a trapezoidal cardboard with an upper base of 3 cm, a lower base of 6 cm, and a height of 4 cm. What is the area of this rectangle in cm**2.
从一个上底3cm、下底6cm、高4cm的梯形纸板上取一个最大的长方形，这个长方形的面积是多少cm**2．
<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<result>12</result>