The upper base of a trapezoid is 5 decimeters, the lower base is 8 decimeters, and the height is 4 decimeters. What is its area?
一个梯形的上底是5分米，下底是8分米，高是4分米，它的面积是多少平方分米．
<gadget id="calculator">5 + 8</gadget>
<output>13</output>

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

<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<result>26</result>