You slap some dough on to a beach and wait for it to become bread
Well, a compound has a total charge of 0. So, it's electrically neutral. Since the X is 3+ and the Y is 3- they add to 0. Meaning no subscripts are necessary. Why don't you try a different combo?
Like:
A^3 and B^1-, to get a 3- charge you need 3xB^1- so the formula is AB3
Does this help?
electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure (e.g., a crystal).
The reaction is a synthesis…

… because <em>two substances are combining to make one other substance</em>.

It is also a <em>reduction-oxidation reaction</em> because the <em>oxidation number of Al increases</em> from 0 to +3 and the <em>oxidation number of O</em> decreases from 0 to -2.