The upper base of a trapezoid is 9 decimeters, the lower base is 10 decimeters, and the height is 4 decimeters. What is the area in square decimeters?
一个梯形的上底是9分米，下底是10分米，高是4分米，面积是多少平方分米．
<gadget id="calculator">9 + 10</gadget>
<output>19</output>

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

<gadget id="calculator">19 * 2</gadget>
<output>38</output>

<result>38</result>