If the sum of the upper and lower bases of a trapezoid is 20 cm and the height is 8 cm, what is the area in square centimeters?
一个梯形的上下底的和是20厘米，高是8厘米，面积是多少平方厘米．
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

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

<result>80</result>