A certain class of students planted a batch of trees in their spare time. They planted all (1/6) of them on the first day, and planted 21 trees on the second day. The remaining (3/2) of the trees planted on the first day were not planted. How many trees are there in total?
某班同学利用课余时间栽一批树，第一天栽了全部的(1/6)，第二天栽了21棵，还剩第一天栽的棵数的(3/2)没栽，这批树共多少棵？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(1/6) * (3/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/6) - (1/4)</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">21 / (7/12)</gadget>
<output>36</output>

<result>36</result>