Please give me your own writting solutions, not other's, thank you!

4. Let n > 15. We are decomposing Kn,n into four spanning subgraphs G1, G2, G3, and G4 with disjoint set of edges. In other words, G; = (V, E;) where E1, E2, E3, E4 are pairwise disjoint and (V, EU E, U E3 UE4) = Kn.n (a) Prove that at least one of G1, G2, G3, or G4 is non-planar. (b) Disprove the previous part for n = 5 by giving a counter-example