The top of a trapezoid is 5 decimeters, the bottom is 7 decimeters, and the height is 6.5 decimeters. What is its area in square decimeters?
一个梯形的上是5分米，下底是7分米，高是6.5分米，它的面积是多少平方分米．
<gadget id="calculator">5 + 7</gadget>
<output>12</output>

<gadget id="calculator">6.5 / 2</gadget>
<output>3.25</output>

<gadget id="calculator">12 * 3.25</gadget>
<output>39</output>

<result>39</result>