Answer
The center of mass moves 4 cm in the +x-direction.
Work Step by Step
Since the y-coordinate of all three points stays the same, the y-coordinate of the center of mass does not change.
Let $M$ be the mass of each object. Let $x_{com}$ be the x-coordinate of the original center of mass. We can find the x-coordinate of the new center of mass $x_{com}'$:
$x_{com}' = x_{com}+\frac{(M)~(12~cm)}{3M} = x_{com}+4~cm$
The center of mass moves 4 cm in the +x-direction.
