How Does Adding Mass Affect Normal Force?

[mystmyst]

I just made up this question to understand how normal force works:

Let's say mass $$A = 20 kg$$ and it's on a flat surface. The normal force = $$20g$$

But what happens when you put mass B on top of mass A?

mass B = $$10kg$$

Does mass A have the same normal force, or does the normal force equal $$20g + 10g$$

And does mass B have it's own normal force reacting on mass A which would equal $$10g$$?

 

[Delzac]

The force acting on block A due to the ground would be 30g. The force that block A acts on block B is 10g.

 

[mystmyst]

Thanks for your quick response!