Task: Question Answering
Input (English): Problem: 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 ?
Options: a. 30, b. 60, c. 75, d. 90, e. 105
Output (English): a