How to estimate the complexity of sequential algorithm given that we know the complexity of each step?

First case: I was stumble upon a two step sequential algorithm where the big O complexity of each step is O(N^9).

Second case: Also if the algorithm have three steps where the complexity of step 1 is O(N^2), the complexity of step 2 is O(N^3) and the complexity of step 3 is O(N^9)

What would be the complexity of the first case and second case ?