The answer is B, C, and D. Like terms are terms with all the same variable, so 5x and -x are like terms.
C is correct. If we add -x to 5x, we get 4x. The other numbers remain unchanged because they have no like terms.
D is correct. Applying the rule of like terms, which is that like terms are numbers with the same variable, only add together numbers with the same variable.
