sphere A has a -4 charge and sphere B has a +2 charge

The charges equalize to –4+2 = –2 units

as long as they are in contact, that same charge of –2 units applies to both spheres.

If they are separated, the distribution of those –2 units depends on the capacitance of each. If they are equal, they both get –1 units.

The total charge stays constant. The total charge is:

-4 + 2 = -2

Divided evenly among two spheres:

-2 / 2 = -1

Therefore, each will have a charge of -1 after contact.

Total charge = (-4) + (+2) = -2 units.

Since the spheres are identical, the charge gets equally split. Each sphere ends up with a charge of -1 unit.

Final charge on sphere A = -1 unit.