Describe the order of growth of each of the following functions using O notation (can you please provide step-by-step solutions, I really dont understand anything related to this topic at all)

a.) N^2 +3N

b.) 3N^2 + N

c.) N^5 + 100N^3 + 245

d.) 3Nlog2N + N^2

e.) 1 + N + N^2 + N^3 + N^4

f.) (N*(N-1)) / 2