please i need help with practice quiz thank you so much

Let f : {1, 2, 3, ... ) - Z be defined by f (n ) = 1 -n if n is even 1 +n ifn is odd a) Is f a one-to-one functions? Answer "YES" or "NO" and justify your answer. b) Is f an onto functions? Answer "YES" or "NO" and justify your answer. c) Let 27 be the set of all even integers, that is, { ..., -6, -4, -2, 0, 2, 4, 6, ... } . Do the sets Z+ and 27 have the same cardinality? Answer "YES" or "NO" and justify your