If you have :

26n^4 + 8n^3ln(n) + 18 n and you want to get the lower bound (gamma) I thought you took the highest level of the polynomial which would make it n^4) but the correct answer is n^3 ln(n). Can anyone set me straight as to why?

another one that makes no sense to me is:

14n^3 + 5nln(n) + 18 has a lower bound of n???? I thought it would be n^3

Thanks for any logic I can use to tackle these on an exam.