4x and 5x are like terms
Like terms will have EXACTLY the same variables...
Example :
2x and 3x are like terms
2x and 3y are not like terms
2x and 2x^2 are not like terms
also, constants are like terms...
8 and 5 are like terms
2x and 5 are not like terms
3y^2 and 6 are not like terms
