trapezoid has an area of 72 square meters and a height of 6 meters. The bottom is 15 meters, how many meters is the top.
一个梯形的面积是72平方米，高是6米．下底是15米，上底是多少米．
<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">72 * (1/3)</gadget>
<output>24</output>

<gadget id="calculator">24 - 15</gadget>
<output>9</output>

<result>9</result>