The concentration of a kind of sugar solution is 10%. After adding 30 grams of sugar, its concentration becomes 15%. How many grams does this sugar solution originally have?
一种糖水的浓度是10%，加入30克糖后，它的浓度变为15%，这种糖水溶液原来有多少克？
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">30 * (3/20)</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">30 - (9/2)</gadget>
<output>51/2 = around 25.5</output>

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

<gadget id="calculator">(3/20) - (1/10) - 1</gadget>
<output>-19/20 = around -0.95</output>

<gadget id="calculator">1 + (-19/20)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(51/2) / (1/20)</gadget>
<output>510</output>

<result>510</result>