A pitfall is expecting to improve the overall performance of a computer by improving only one aspect of the computer. Consider a computer running a program that requires $250$ s$,$ with $70$ s spent executing FP instructions, $55s$ executed ALU instructions, $85s$ executed load$/$store instructions, and $40s$ spent executing branches instructions.

a$.$ By how much is the total time reduced if the time for FP operations is reduced by $20\%?$

b$.$ Can the total time can be reduced by $20\%$ by reducing only the time for branch instructions? Why?