Mergesort
•Remember, each one of these calls requires 3*M-1 operations, where M starts equal to N, then becomes N/2.
•When M = N/2, there are actually 2 calls to merge, so there are 2*(3*M-1) operations or 6(N/2)-2  =>>>>> 3N-2.
•Expanding on this: at recursive call m, there are 2m calls to re-merge where each call merges N/2m elements, so it requires 3*(N/2m )-1 operations.