I'm having problems calculating the complexity of the following recurrence equation.

It's quite difficult for me to solve it. Could anyone help me to solve this problem? Thanks in advance.
I'm having problems calculating the complexity of the following recurrence equation.

It's quite difficult for me to solve it. Could anyone help me to solve this problem? Thanks in advance.
This is the same recurrence for the average case complexity of quicksort with solution
T(n)=O(n log n)