In worst case, number of comparisons to merge two sorted lists of size m and n is m+n-1.
We take two lists of size 8 each, and merge them into a list of size 16. Comparisons needed = 8+8-1 = 15.
Similarly, to merge the other two lists of 8 elements, comparisons needed = 15.
We have two lists of size 16 and 16 now.
To merge them to a list of size 32, number of comparisons needed = 16+16-1 = 31.
Total comparisons = 15 + 15 + 31 = 61.
NOTE: In best case, we need max(m,n) comparisons. It happens when the last element of the first list is smaller than the first element of the second list.
