A trapezoid, the sum of the upper and lower bases is 12.8 cm, and the height is 8 cm, what is its area?
一个梯形，上底和下底的和是12.8cm，高是8cm，它的面积是多少．
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">12.8 * 4</gadget>
<output>51.2</output>

<result>51.2</result>