The upper base of a trapezoid is 5 cm, and the lower base is 8 cm. The difference between the upper and lower bases is its height. What is the area of the trapezoid?
一个梯形的上底是5厘米，下底是8厘米，上下底的相差数就是它的高，这个梯形的面积是多少？
<gadget id="calculator">5 + 8</gadget>
<output>13</output>

<gadget id="calculator">8 - 5</gadget>
<output>3</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">13 * (3/2)</gadget>
<output>39/2 = around 19.5</output>

<result>39/2 = around 19.5</result>