The sum of the upper and lower bases of a trapezoid is 20 cm, which is 5 times the height. What is the area of the trapezoid in cm**2.
一个梯形上底和下底的和是20厘米，是高的5倍，这个梯形的面积是多少cm**2．
<gadget id="calculator">20 / 5</gadget>
<output>4</output>

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

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>