\(M\left(t\right)+A\left(t\right)=\left(t^2-8\right).\left(-3\right)t\)
\(\Rightarrow M\left(t\right)=-A\left(t\right)+\left(t^2-8\right).\left(-3\right)t\)
\(\Rightarrow M\left(t\right)=-\left(t^4-7\right)+\left(-3t^3+24t\right)\)
\(\Rightarrow M\left(t\right)=-t^4-3t^3+24t+7\)