To find the total charge, it seems we should add the charge of protons and electrons here.
Aluminum: (-10) + 13 = 3
Aluminum has an overall charge of +3.
Phosphide: (-18) + 15 = -3
Phosphide has an overall charge of -3.
Iodide: (-54) + 53 = -1
Iodide has an overall charge of -1.
Tin: (-50) + 50 = 0
Tin has an overall charge of 0.