Your notation is somewhat ambiguous since you don't separate multiplication and power-of clearly.
Still the Ordo complexity of an expression is determined by the fastest growing term when N approaches infinity. In my view you've got it wrong in the third and fourth example. They should be O(logN) and O(N^3) respectively.
O(logN) and O(N^3) for third and fourth this is true answer?
Yes, I would say so. The Ordo complexity is determined by the term that grows the fastest asymptotically. And that's the term you picked in all cases except in 3 and 4. In 3 it's log(n) and in 4 it's n^3 so these will determine the complexity.
But don't take what I say at face value. After having studied software engineering for 3 years at a university you should know this better than I do.
hmmm, what about part B bro?
Yes what about it? If you suggest something with a motivation I'll tell you what I think.