In a group of ducks and cows, the total number of legs are 40 more than twice the number of heads. Find the total number of cows.
Choose one:
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 40 more than twice the number of heads = > 2 ( d + 2 c ) = 40 + 2 ( c + d ) = > d + 2 c = 20 + c + d = > 2 c = 20 + c = > c = 20 i . e . , total number of cows = 20 answer is e ."
Answer: E