Xiao Li's family planted 15 mango trees, the number of lychee trees is 2/3 of mango trees, and 2/7 of longan trees. How many longan trees does Xiaoli's house have?
小莉家种了15棵芒果树，荔枝树的棵数是芒果树的(2/3)，又是龙眼树的(2/7)．小莉家有多少棵龙眼树？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(2/3) / (2/7)</gadget>
<output>7/3 = around 2.333333</output>

<gadget id="calculator">15 * (7/3)</gadget>
<output>35</output>

<result>35</result>