At Deluxe paint store, Fuchsia paint is made by mixing 6 parts of red paint with 3 parts of blue paint. Mauve paint is made by mixing 4 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? Pick.
A) 9  B) 12  C) 15  D) 16  E) 18

Rationale: in 24 liters , red = 6 / 9 * 24 = 16 and blue = 8 so , 16 / ( 8 + x ) = 4 / 5 or , x = 12 ( answer b )
Answer: B