4 men and 12 boys finish a piece of work in 4 days, 7 men and 6 boys do it in 5 days. The ratio between the efficiencies of a man and boy is?  Options.
A) 18 : 19  B) 17 : 19  C) 15 : 19  D) 18 : 14  E) 18 : 11

Rationale: "4 m + 12 b - - - - - 4 days 7 m + 6 b - - - - - - - 5 days 16 m + 48 b = 35 m + 30 b 18 b = 19 m = > 5 m = 6 b m : b = 18 : 19 answer : a"
Answer: A