A is made up of 4 regions d, e, f, and g

Why 4?  Because 
1. d is the part of A which is not part of B or C,
2. e is the part of A which is also part of B but not part of C.
3. g is the part of A which is also part of C but not part of B.
4. f is the part of A which is also part of B and C.

That's all you asked but you need to know the
following as well:

B is made up of 4 regions e, f, h, and i
C is made up of 4 regions f, g, i, and j

Region d is part of A but is not part of B or C
Region h is part of B but is not part of A or C
Region j is part of C but is not part of A or B

Region e is part of A and B, but is not part of C
Region g is part of A and C, but is not part of B
Region i is part of B and C, but is not part of A

Region f is part of A, part of B, and part of C

Region k is not part of any of A, B or C.




Edwin