Two objects being pushed by one force what is the force on the second? object

[nyjets2428]

A block of mass 4.0 kg lies on a frictionless horizontal table in contact with a 6.0 kg block. At the opposite side of the 4.0 kg block, a constant horizontal force of 100.0 N is applied as shown in the diagram. What is the magnitude of the horizontal force on the 6.0 kg block?

I do not know where to start with this. I am confused on how this would work. I understand that the 4 kg blocks force will be pushing the 6 kg block. but how do i figure this out

 

[Simon Bridge]

Draw free body diagrams for each block separately.
Call the contact force between the blocks R.

For each block, write Ʃforces = ma.
This should give you two equations and two unknowns.