What is the algebraic expression for N cubed increased by 5?

It is ##n^3 + 5##

The hard part of this is translating the English words into algebraic expressions.

"n" is a variable. So we start with that: ##n##

"cubed" means raising to the power of 3. So we put an exponent in the top-right corner of the variable: ##n^3##

"increased by" means "plus", so we put a plus sign, and then the number 5: ##n^3 + 5##