There are two pools, A and B. Originally, the volume of water in pool B is less than that of pool A (1/6). Now, after injecting (1/5) of the water in pool A into pool B, C draws 21 cubic meters of water from pool B. At this time, the amount of water in the two pools is exactly the same. How many cubic meters of water was originally in the second pool?
甲、乙两个水池，原来乙水池水量比甲少(1/6)，现在把甲池中的水的(1/5)注入乙池后，丙从乙池抽走21立方米的水，这时两个池中水量恰好同样多，乙池中原来有水多少立方米．
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 - (1/6)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(5/6) + (1/5)</gadget>
<output>31/30 = around 1.033333</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(31/30) - (4/5)</gadget>
<output>7/30 = around 0.233333</output>

<gadget id="calculator">21 / (7/30)</gadget>
<output>90</output>

<gadget id="calculator">90 * (5/6)</gadget>
<output>75</output>

<result>75</result>