Please help me solve this problem. Please only solve if you are 100 percent sure and please show as much steps as possible, Thank you very much for your help

3, (10%) Given an input list of n numbers, recall that Mergesort first divides the list into two parts, then sorts each part recursively, and finally merges the two sorted parts together. The running time of Mergesort is (n log n). Now suppose that we divide the input list into three parts, sort each part recursively, and finally merge the three sorted parts together (how?). Will this new algorithm run faster or slower in the asymptotic sense? Why