Like terms:

3x + 4x = (3+4)x = 7x

Unlike terms:

3x + 4x^2 (cannot be combined. The best you can do is factor out an x: (3+4x)x.)

3x + 4x = (3+4)x = 7x

Unlike terms:

3x + 4x^2 (cannot be combined. The best you can do is factor out an x: (3+4x)x.)