The average length of the upper and lower bases of a trapezoid is 40 cm, and the height is 12 cm. What is the area of the trapezoid in square centimeters?
一个梯形的上底与下底的平均长度是40厘米，高是12厘米，这个梯形的面积是多少平方厘米．
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">40 * 2 * 6</gadget>
<output>480</output>

<result>480</result>