The ratio of poplars to willows in the campus is 3:5. There are 18 poplars. How many willows are there?
校园里杨树与柳树的棵数比是3：5，杨树有18棵，柳树有多少棵？
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">18 / (3/5)</gadget>
<output>30</output>

<result>30</result>