The sixth grade students went to plant trees. The first class planted 49 trees. The tree planted by the second class was from the first class (5/7), and the tree planted by the third class was from the second class (4/5). How many trees were planted by the third class? tree?
六年级同学去植树，一班植了49棵，二班植的棵树是一班的(5/7)，三班植的棵树是二班的(4/5)，三班植了多少棵？
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">49 * (5/7) * (4/5)</gadget>
<output>28</output>

<result>28</result>