After adding 30 grams of water to 15% salt water, the concentration of the salt water becomes 10%, how many grams of salt does the salt water contain?
向浓度15%的盐水中加入30克的水后，盐水浓度变为10%，问盐水中含有多少克盐？
<gadget id="calculator">30 / 1</gadget>
<output>30</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">0 / 100</gadget>
<output>0</output>

<gadget id="calculator">(1/10) - 0</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(3/20) - (1/10)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/10) / (1/20)</gadget>
<output>2</output>

<gadget id="calculator">30 * 2 * (3/20)</gadget>
<output>9</output>

<result>9</result>