To subtract fractions, we need to find a common denominator. In this case, the common denominator is 7. So, we convert the whole number 6 to a fraction with a denominator of 7, which is 42/7. Thus, the equation becomes 42/7 - 4/1. Subtracting the fractions, we get 38/7. Simplifying this fraction, we get 5 and 3/7, which can be written as 5 3/7. Therefore, the correct answer is 5 3/7, which is equivalent to 2 5/7.