The sum of the upper and lower bases of a trapezoid is 2.5dm, and the height is 4dm. What is the area of the trapezoid in dm**2.
一个梯形上底与下底的和是2.5dm，高是4dm，这个梯形的面积是多少dm**2．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2.5 * 2</gadget>
<output>5</output>

<result>5</result>