3 move 12 unit lengths to the left and 8 unit lengths to the right on the number axis. How many unit lengths can this number move to the right to return to the origin? Is the origin 0 or 3?

3 move 12 unit lengths to the left and 8 unit lengths to the right on the number axis. How many unit lengths can this number move to the right to return to the origin? Is the origin 0 or 3?

Take the right as the positive direction
Then 12 units to the left, length = - 12
Right 8 units length = + 8
Then - 12 + 8 + x = 0
x=4