Change the mixed fractions to an improper fraction.
4 5/7 = 32/7
1 6/7 = 13/7
Now you can easily subtract since both fractions have common denominators
32/7 - 13/7
(Think: 32 - 13 = 19)
Change the improper fraction to a mixed fraction
19/7 = 2 5/7
Answer: 2 5/7
Hope I helped =)