Compute the sum and product of $p(x)$ and $q(x)$
(a) $p(x)=1+x+2 x^{2}, q(x)=3 x^{2}+x^{3},$ where both polynomials are in $\mathbb{Z}_{5}[x]$.
(b) $p(x)=1+4 x^{2}+3 x^{3}+2 x^{4}, q(x)=5+2 x^{2}+x^{3},$ where both polynomials are in $\mathbb{Z}_{6}[x]$.