The sum of the upper and lower bases of a trapezoid is 7dm, the height is 4dm, what is the area dm**2.
一个梯形的上下底的和是7dm，高是4dm，面积是多少dm**2．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">7 * 2</gadget>
<output>14</output>

<result>14</result>