Using the merge algorithm.. If one sorted list has m elements and another has n elements then it requires m+n-1 comparisons during merging of list in worst case...
There are four list of 8 elements.. First two list requires 8+8-1=15 comparison and another two list requires 8+8-1=15 comparison.. Now we have two list of 16 elements, the number of comparison required is 16+16-1=31 comparison..
Total we have 15*2+31=61 comparison