It's a REGULAR language,.
If n>=1 or anything it's just a (a+b)*
Now, you have choice to take n as any number.
Consider every string as a part of
(a+b)* and if n>=1 then start string with 'a' and End that string with just 'b' and if n>=0 then it's simply a (a+b)*
(Like we do this in palindrome's sums)
FA:
(a,b)--a-->(a,b)--b-->()
For eg. String is bababaabb
(bab) a (baab) b