At Deluxe paint store, Fuchsia paint is made by mixing

[apps132033]

At Deluxe paint store, Fuchsia paint is made by mixing 5 parts of red paint with 3 parts of blue paint. Mauve paint is made by mixing 3 parts of red paint with 5 parts blue paint. How many liters of blue paint must be added to 24 liters of Fuchsia to change it to Mauve paint?

A) 9
B) 12
C) 15
D) 16
E) 18

Having trouble with ratio parts-to-parts questions. Please help.
Source: Chili Hot GMAT Math Review

[RonPurewal]

hi,
welcome to the forum (i see that this is your first post). but, remember, this forum isn't meant to be an "answer key" for random problems that people post here -- it's meant to be a place where specific questions are answered.

i.e., please don't just post a problem. instead, tell us what you've already tried.
what did you understand?
how did you try to set up the problem?
where did you get stuck?
what other methods did you try?
etc.

once you've outlined the steps you've already taken, we can give some input that will actually help you solve future problems. (if we just provide an answer key, there's very little utility in that -- and besides, i'd guess, the problem most likely has an answer key already.)