I think the below language is Regular-
L = {xy | na(x) = nb(y) where x,y $\in$ (a,b)* }
Doubt : Since if we consider any string in given language is split in such a way so that we satisfy the required condition. like
(abbbaa)(bbaba), (bbbbb)(a) etc.
(Note - brackets are just for understanding purpose). Can some one write the regular grammar for this language?