What is the upper found or Big O notation for the given functions

5^n and 1.1^n are exponential (growing) functions. They grow asymptotically faster than any polynomial function, which n^3 and n^2 are. (This can be proven e.g. via l'Hôpital.)

Therefore the functions are Theta(5^n) and Theta(1.1^n) respectively. Note that these classes are not the same, since an exponential function with a larger base/rate asymptotically dominates one with a smaller base/rate.

Big O notation is a mathematical notation that describes the limiting behavior of a function when the argument tends towards a particular value or infinity.

So as you can see, so the first function behave asymptotically like 5^n, since the lower order terms when n tends to infinity are negligible. And the second one is dominated by 1.1^n since is an exponential function and 1.1 > 1.