Cannot be simplified because the first term is to the second degree while the other is to the third so they are not like terms.
Work Step by Step
Terms can only be combined by addition and subtraction if they are like terms. For terms to be alike they have to have the same variables and they have to be of the same power. In this case one x is to the 2nd power while the other is to the 3rd power so they are not like terms and they cannot be combined.