The upper base of a trapezoid is 2.5 decimeters long, the lower base is 3.5 decimeters long, and the height is 4 decimeters. What is the area in square decimeters?
一个梯形的上底长2.5分米，下底长3.5分米，高4分米，面积是多少平方分米．
<gadget id="calculator">2.5 + 3.5</gadget>
<output>6</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<result>12</result>