4. Consider sorting n = 6 real-valued keys. Compute the worst-case number of key comparisons (exact number, not order) for each of the following cases. Show the work. (a) Insertion sort (b) Mergesort (Assume recursive implementation of mergesort.) Show the merge tree. Show the number of comparisons for each merge, and compute the total. (c) What is the theoretical lower bound on the worst-case number of comparisons? (Give the exact worst-case number.) How does this lower bound number compare with the above upper bounds