Find Context free grammars (CFG). Theoretical computer science. Please help

Find context free grammars for the following languages (a) L = {a^n b^m: n, m greaterthanorequalto 0 and n notequalto m} (b) L = {a^n b^m c^k: n greaterthanorequalto m greaterthanorequalto 0 or m greaterthanorequalto k greaterthanorequalto 0} (c) L = {a^n b^m c^k: n + m > k > 0} (d) L = {a^n b^m a^i b^j: n + m notequalto i + j} (e) L = {w elementof {a, b, c}*: n_b (w) = n_a(w) + n_c(w)} (f) L = {w elementof {a, b, c}*: n_b(w) notequalto n_a(w) + n_c(w)}