The average length of the upper and lower bases of a trapezoid is 20 cm, and the height is 16 cm. What is its area in square centimeters?
一个梯形的上、下底的平均长度是20厘米，高是16厘米，它的面积是多少平方厘米．
<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">20 * 2 * 8</gadget>
<output>320</output>

<result>320</result>