In a group of ducks and cows, the total number of legs are 30 more than twice the number of heads. Find the total number of cows.  Choose the correct option
A) 12 B) 15 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 28 more than twice the number of heads = > 2 ( d + 2 c ) = 30 + 2 ( c + d ) = > d + 2 c = 15 + c + d = > 2 c = 15 + c = > c = 15 i . e . , total number of cows = 15 answer is b ."
Answer: B