The upper base of a trapezoid is 2.8dm, the lower base is 3dm, and the height is 4dm. What is the area in dm**2.
一个梯形的上底是2.8dm，下底3dm，高4dm，面积是多少dm**2．
<gadget id="calculator">2.8 + 3</gadget>
<output>5.8</output>

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

<gadget id="calculator">5.8 * 2</gadget>
<output>11.6</output>

<result>11.6</result>