The area of the trapezoid is 480 square centimeters, the height is 20 centimeters, the upper base is 30 cm, and the length of the lower base is in centimeters.
梯形的面积是480平方厘米，高是20厘米，上底30厘米，下底长多少厘米．
<gadget id="calculator">2 / 20</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">480 * (1/10)</gadget>
<output>48</output>

<gadget id="calculator">48 - 30</gadget>
<output>18</output>

<result>18</result>