In this situation three blocks are initially at rest on a table.
The red block weighs 4 N
The green block weighs 6 N
The blue block weighs 5 N
A hand then applies a constant force, to the right, on the red block. All three blocks accelerate to the right.
Draw the free-body diagrams of each block. When drawing a free-body diagram the key is to isolate one part of the system and draw all the forces being applied to that one part.