Question 459531
Let x=amount of pure acetic acid needed
Now we know that the amount of pure acetic acid that exists before the mixture takes place (x+0.30*10) has to equal the amount of pure acetic acid after the mixture takes place (0.60(x+10)).   Sooooo
x+0.30*10=0.60(x+10) get rid of parens and simplify
x+3=0.60x+6 subtract 3 and also 0.60x from each side
x+3-3-0.60x=0.60x-0.60x+6-3  collect like terms
0.40x=3
x=7.5 liters----------------amount of pure acetic acid needed

CK
7.5+0.30*10=0.60*17.5
7.5+3=10.5
10.5=10.5

Hope this helps---ptaylor