On a certain farm the ratio of horses to cows is 4:1. If the farm were to sell 15 horses and buy 15 cows, the ratio of horses to cows would then be 7:3. After the transaction, how many more horses than cows would the farm own?  Choose the correct choice from the following answers
A) 20  B) 40  C) 50  D) 60  E) 80
Originally, there were 4k horses and k cows.   3(4k-15) = 7(k+15)   12k-7k = 105+45   5k = 150   k = 30   The difference between horses and cows is (4k-15)-(k+15) = 3k-30 = 60   The answer is 60.
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On a certain farm the ratio of horses to cows is 4:1. If the farm were to sell 15 horses and buy 15 cows, the ratio of horses to cows would then be 7:3. After the transaction, how many more horses than cows would the farm own?