The sum of the upper and lower bases of a trapezoid is 20cm, the height of the trapezoid is 8cm, what is the area in cm**2.
一个梯形的上底与下底的和是20cm，梯形的高是8cm，面积是多少cm**2．
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<result>80</result>