How many grams of 4% brine has evaporated and turned into 10% brine, then add 300 grams of 4% brine to make it 6.4% brine, how many grams is the initial brine?
有若干克4%的盐水蒸发一些水分后变成了10%的盐水，再加进300克4%的盐水，混合变为6.4%的盐水，问最初的盐水是多少克？
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">300 * (1/10)</gadget>
<output>30</output>

<gadget id="calculator">4 / 100</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">30 / (1/25)</gadget>
<output>750</output>

<result>750</result>