The existing mass fraction is 80 grams of salt water with 20%. How many grams of salt need to be added to turn these salt water into salt water with a mass fraction of 75%?
现有质量分数为20%的食盐水80克．把这些食盐水变为质量分数为75%的食盐水，需要再加食盐多少克？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">80 * (4/5)</gadget>
<output>64</output>

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

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">64 / (1/4)</gadget>
<output>256</output>

<gadget id="calculator">256 - 80</gadget>
<output>176</output>

<result>176</result>