There are 15 cypress trees in the campus. The willow trees are cypress trees (3/5) and pine trees (1/3). How many pine trees are there?
校园里有柏树15棵，柳树的棵树是柏树的(3/5)，又是松树的(1/3)，松树有几棵？
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(3/5) / (1/3)</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">15 * (9/5)</gadget>
<output>27</output>

<result>27</result>