Part $2$: Amdahl's Law $(10$ points$)$

$[5$ pts$]$ Suppose that we can improve the floating$-$point instruction performance of a machine by a factor of $15($the same floating$-$point instructions run $15$ times faster on this new machine$).$ What percent of the instructions must be floating point to achieve a speedup of at least $4?$

$[5$ pts$]$ Suppose a program runs in $100$ seconds on a machine, with multiply responsible for $80$ seconds of this time. How much do we have to improve the speed of multiplication if we want the program to run $4$ times faster?" How about making it $5$ times faster?