Teacher Wang plans to dilute 30 grams of 85% alcohol to 75% alcohol, how many grams of water should be added?
王老师计划把30克85%的酒精稀释成75%的酒精，应加多少克水？
<gadget id="calculator">85 / 100</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(17/20) / (3/4)</gadget>
<output>17/15 = around 1.133333</output>

<gadget id="calculator">30 * (17/15)</gadget>
<output>34</output>

<gadget id="calculator">34 - 30</gadget>
<output>4</output>

<result>4</result>