what is 18x^3+6x^3?

This is just a simple expression to simplify

18x^3 + 6x^3 = 24x^3

Because both the base (x) and the exponent (3) are the same in both terms of the original expression we can simply add them to simplify them.

If you are given a value for (x) you can evaluate the expression

24x^3

18x^3 + 6x^3
= 24x^3

18 apples + 6 apples = 24 apples
18 x³ + 6 x³ = 24 x³

18x^3+6x^3 =
(18 + 6)x^3 =
24x^3

24x^3
Explaination:
take x^3 common

x^3(18+6) = 24 x^3

It's 24x³

That's all you can do with it.