Answer:
3x+3
Explanation
Like terms are terms that contain the same variables raised to the same power. As such in your equation you would combine the 4x and the -x because they contain the same variable (x). To combine these terms you simply add 4x + - x, which can be written as 4x - x. The product of this is 3x. Because there is a 3 on its own with no other like terms to add to it the it, the simplified version of this equation would be 3x+3.