The school has planted a batch of saplings, which have already planted (2/5) of the total number. If 21 more trees are planted, then (3/4) of the total number has been planted. How many saplings are there in this batch?
学校栽种一批树苗，已经栽了总数的(2/5)，如果再栽21棵，则正好栽了总数的(3/4)，这批树苗共有多少棵？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/4) - (2/5)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">21 / (7/20)</gadget>
<output>60</output>

<result>60</result>