Throcial computer science, just do b,c,d

Find context free grammars for the following languages (a) L = {a")" : n,m> 0 and n #m} (b) L = {abmck:n > m > 0 or m > k >0} (c) L = {abmck: n + m > k >0} (d) L = {w {a,b,c}* : n6(w) = na(w) + nc(w)}