Two Boys with Masses of 40 Kg and 60 Kg

Multiple Choice

Two boys with masses of 40 kg and 60 kg stand on a horizontal frictionless surface holding the ends of a light 10-m long rod.The boys pull themselves together along the rod.When they meet the 40-kg boy will have moved what distance?

A) 4 m
B) 5 m
C) 6 m
D) 10 m
E) need to know the forces they exert