linear equation word problem: mixing paints

[trish12345]

okay, you have 2.687492 liters of paint. you go to the store, they have a special on paint with 7% color included. you dont want that bright of a color, instead only 3% of the color. how much 7% paint do you buy to mix with plain white paint to get your 3% mixture. what is the amount of 7% paint? what is the amount of pure white paint? i think somehow you are supposed to use the substitution method but i cant quite configure it into an equation. please help.

 

[stapel]

okay, you have 2.687492 liters of paint. you go to the store, they have a special on paint with 7% color included. you dont want that bright of a color, instead only 3% of the color. how much 7% paint do you buy to mix with plain white paint to get your 3% mixture. what is the amount of 7% paint? what is the amount of pure white paint? i think somehow you are supposed to use the substitution method but i cant quite configure it into an equation.

Multi-post.

(Note to tutors: There is much more information at the other location, though much still appears to be missing.)