Assume a program requires the execution of $100$ x $106$ FP instructions, $220$ x $106$ INT instructions, $160$ x $106$ L$/$S instructions and $32$ x $106$ Branch instructions. The CPI for each type of instruction is $2,2,8,$ and $4,$ respectively. Assume that the processor has a $4$ GHz clock rate.

By how much must the CPI of L$/$S instructions be improved if the program is to run four times faster?

a$)$ What is the execution time of the program for computer A$?$

b$)$ What is the execution time for computer B$?$

c$)$ What is the average CPI for computer B if the average CPI for computer A is $2?($Note: You have to assume that both computer systems execute the same number of instructions$)$