In a group of ducks and cows, the total number of legs are 36 more than twice the number of heads. Find the total number of cows.	Choose the correct answer:  A) 12  B) 14  C) 16  D) 18  E) 20

Rationale: "let the number of ducks be d and number of cows be c then , total number of legs = 2 d + 4 c = 2 ( d + 2 c ) total number of heads = c + d given that total number of legs are 36 more than twice the number of heads = > 2 ( d + 2 c ) = 36 + 2 ( c + d ) = > d + 2 c = 18 + c + d = > 2 c = 18 + c = > c = 18 i . e . , total number of cows = 18 answer is d ."
Answer: D