Question $(1)$

For the following Characteristic equation, Use routh$-$Hurwitz stability criteria to determine if it is stable or not.

$($a$)(10$ points$)s^4+6s^3+4s^2+2s+1=0$

$($b$)(10$ points$),s^5+4s^4-3s^3+2s^2+s+6=0$

$($c$)(10$ points$)3s^3+18s^2+3s+6=0$