Question 155744
Let x=amount of water required

Now we know that the amount of pure dye before the water is added(0.12*15) has to equal the amount of pure dye after the water is added(0.05(15+x))
So, our equation to solve is:

0.12*15=0.05*(15+x) get rid of parens and simplify
1.8=0.75+0.05x  subtract 0.75 froom each side
1.8-0.75=0.75-0.75+0.05x  collect like terms
1.05=0.05x divide each side by 0.05
x=21 liters-----------------------------amount of water needed

CK
0.12*15=0.05*36
1.8=1.8

Hope this helps---ptaylor