Answer:
Okay so all you need to know is the percentage of the hydrogen peroxide. 
We know that the total solution is 400 ml and the hydrogen peroxide solution is 8ml. 
8/400 
Percent means out of a hundred, this can go multiple ways. 
<u>Way #1, benchmarking.</u>
So 8/400 simplified is 1/50 or 2/100. 
1/50 is basically 2/100. 
And percent means out of a hundred so 2/100 is basically 2percent. 
<u>Way #2, proportions</u>
We want to know the percentage of hydrogen/ fabric dye
If you put it in numbers int he same fraction and put “x” as the unknown 8ml hydrogen peroxide solution you’d get. 
8/400 = x/100 
X/100 because percent means out of a hundred. 
Now solve3
Cross multiply,
800 = 400x 
divide 400 on both sides 
2=x 
Now plug it back in the proportion. 
8/400 = 2/100 
If you simplify to check if they are equal then it’s correct