There are 60 grams of pure alcohol, how many grams of water need to be added to prepare a 75% alcohol solution.
有纯酒精60克，配制浓度为75%的酒精溶液需加水多少克．
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">60 / (3/4)</gadget>
<output>80</output>

<gadget id="calculator">80 - 60</gadget>
<output>20</output>

<result>20</result>