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 13:7. After the transaction, how many more horses than cows would the farm own?  Choose the correct answer
A) 30	B) 60	C) 75	D) 90	E) 105
Originally, there were 4k horses and k cows.   7(4k-15) = 13(k+15)   28k-13k = 195+105   15k = 300   k = 20   The difference between horses and cows is (4k-15)-(k+15) = 3k-30 = 30   The answer is 30.
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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 13:7. After the transaction, how many more horses than cows would the farm own?