The area of a trapezoid is 480 square centimeters, the height is 20 centimeters, the bottom is 18 centimeters, how many centimeters is the top?
一个梯形的面积是480平方厘米，高是20厘米，下底是18厘米，上底是多少厘米？
<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 - 18</gadget>
<output>30</output>

<result>30</result>