The upper base of the trapezoid is 5cm, which is half of the lower base, and the height is 0.8 times of the upper base. What is the area of the trapezoid?
梯形的上底是5cm，是下底的一半，高是上底的0.8倍，该梯形的面积是多少．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">5 + 10</gadget>
<output>15</output>

<gadget id="calculator">5 * 0.8</gadget>
<output>4</output>

<gadget id="calculator">(1/2) * 15 * 4</gadget>
<output>30</output>

<result>30</result>