How do you calculate a tight bound run time for these relations?

How do you calculate a tight bound run time for these relations?T(n)=T(n-3)+n^2T(n) = 4T(n/4)+log^3(n)For the first one I used the substitution method which gave me n^2 but wasn't right and the second one I used Masters Theorem and got nlog^4(n) which also wasn't right. A thorough explanation would be helpful. Thanks!