You can calculate the total number of atoms by multiplying the subscripts by the element. I will use the first example to explain this.
Fe2(SO3)3
- Fe has the subscript 2, so there are 2 Fe atoms
- The subscript 3 (after the SO3 bracket) will be multipled in, so multiple everything in the bracket by 3
- S has no subscript after it, so it contains one atom. However, due to the subscript 3 after the bracket, we multiple this by 3. So S has 3 atoms.
- O has a 3 subscript after it, so it contains 3 atoms. However, we have to make sure to multiple it by 3. Therefore, O will have 9 atoms.
If we add all these values we will get the total number of atoms. 2 + 3 + 9 = 14. Therefore, the total number of atoms is 14.