Correct answer is O(n log (base 4/5) n) so according to ans it would be O(n logn)
Here T(n) = O(n) + T(n/5) + T(4n/5)
T(n) = Cn+T(n/5)+T(4n/5) here
we will make recurrence tree between which will be between n/5 and 4n/5
and you will get n/(4n/5)^k = 1
k = log (base 4/5) n
so Cn* (log (base 4/5) n) = o(nlogn)