How many gallons of milk that is 10 percent butter-fat must be added to 8 gallons of milk that is 40 percent butterfat to obtain milk that is 20 percent butterfat?
Answers:  A) 6  B) 12  C) 14  D) 16  E) 28

Rationale: "equate the fat : 0.1 x + 0.4 * 8 = 0.2 ( x + 8 ) - - > x = 16 . answer : d ."
Answer: D