Red Star Farm has 840 apple trees, the number of pear trees is apples (2/7), and oranges (3/8), how many orange trees are there?
红星农场有苹果树840棵，梨树的棵数是苹果的(2/7)，是橘子的(3/8)，橘子树有多少棵？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">(2/7) / (3/8)</gadget>
<output>16/21 = around 0.761905</output>

<gadget id="calculator">840 * (16/21)</gadget>
<output>640</output>

<result>640</result>