What value could you write in after 3x that would make the equation true for all values of x?

3x + 8 = 3x + []

Subtract 3x from both sides.

[] = 8

If you want no values of x, it can be any positive value other than 8. If you want all values of x, the value must be 8. If you want only one value of x, it is impossible because both equations have the same slope.

The answer is 8 because when your balancing equations, both sides of the equation must be equal.