Three Identical 6

Three identical 6.0-kg cubes are placed on a horizontal frictionless surface in contact with one another.The cubes are lined up from left to right and a force is applied to the left side of the left cube causing all three cubes to accelerate to the right at 3.0 m/s².What is the magnitude of the force exerted on the right cube by the middle cube in this case?

A) 12 N
B) 18 N
C) 24 N
D) none of the above