The upper base of the trapezoid is 5 cm, the lower base is 15 cm, and the height is 8 cm. What is the area of the trapezoid in square centimeters?
梯形的上底是5厘米，下底是15厘米，高是8厘米那么梯形的面积是多少平方厘米．
<gadget id="calculator">5 + 15</gadget>
<output>20</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

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

<result>80</result>