4. (3 points) Suppose that unity feedback is to be applied around the listed open-loop systems. (a) G(s) 4+2) (a) G(s) =s(s3 +2s2+3s+4) 2(s+4) (b) G(s) = s2(s+1) (c) G(s) =+2,2-s-1) 4(s3+2s+s+1) Use Routh's stability criterion to determine whether the resulting closed-loop systems will be stable