A trapezoidal billboard, the sum of the upper and lower bases is 40dm, and the height is 1.2m. What is the area of this trapezoidal billboard?
一种梯形广告牌，上底和下底的和是40dm，高是1.2m．这块梯形广告牌的面积是多少平方分米？
<gadget id="calculator">1.2 * 10</gadget>
<output>12</output>

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

<gadget id="calculator">40 * 6</gadget>
<output>240</output>

<result>240</result>