1021. The aggregate of the adjustment payments is equal to the aggregate of the amounts deducted or withheld under subsection 1 of section 1020, during a taxation year, from the sums due to individuals who, on the last day of that year, resided in another province mentioned in section 1020; the Minister shall determine the portion of the amount deducted or withheld under section 1020 which is paid to the government of another province and that which is paid to the government of Canada, as an adjustment payment.