Need help with the following question

Consider the relation R(x, y) = "x and y have the same digitsum" over the natural numbers. The digitsum of a number is the sum of its digits, e.g. digitsum(3079) = 19 and digitsum(2001) = digitsum(111). a) ' Argue that R is an equivalence relation (verify all three required properties). b) What are the equivalence classes of R? Hint: they are nearly all infinite, so simply show the first couple of elements of some of them