On a certain farm the ratio of horses to cows is 6:1. If the farm were to sell 15 horses and buy 15 cows, the ratio of horses to cows would then be 3:1. After the transaction, how many more horses than cows would the farm own?
Choose the correct choice from the following answers: A) 40 B) 50 C) 60 D) 70 E) 80
Originally, there were 6k horses and k cows.   (6k-15) = 3(k+15)   6k-3k = 45+15   3k = 60   k = 20   The difference between horses and cows is (6k-15)-(k+15) = 5k-30 = 70   The answer is 70.
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On a certain farm the ratio of horses to cows is 6:1. If the farm were to sell 15 horses and buy 15 cows, the ratio of horses to cows would then be 3:1. After the transaction, how many more horses than cows would the farm own?