$4$ a$)$ Use merge sort to sort $6,5,17,15,16,20,18,7$ into increasing order.$$ Show all the steps in the algorithm $($draw the trees as shown in class$)($Binary Trees$).$

b$)$ What is the number of comparisons used in the merge algorithm shown in class to merge the two lists: $5,6,7,12,15$; and $1,2,9,14,16.$

c$)$ In the merge algorithm, two lists in increasing order are merged into one $($longer$)$ list of increasing order.$$ Suppose two $($sorted$)$ lists are merged, one has $5$ elements, the other has $6.$ What is the least possible number of comparisons, and when does that occur?$$ What is the maximum possible number of comparisons?