Assume a computer system named $x.$ We would like to improve its performance and name this next$-$generation computer system Y$.$ The part we would like to improve is multiplication that accounts for $80\%$ of the execution time.

$($a$)[7\%]$ Suppose the execution time for multiplication in the new machine is cut into one half. What is the speedup of computer Y compared to computer $x?$

$($b$)[7\%]$ If we want to have the speedup ratio $2?$ How much reduction for the multiplication should we get?