Long-term Debt ($ in millions) 2022 2021 4% debentures, $50 million face value, due in 2028, effective rate 2.5% $15.6 $13.6 Zero coupon bonds, $85 million face value, due in 2030, effective rate 6% $47.7 $42.6 Mortgage debt, $124 million face value, due in 2040, effective rate 3% $87.7 $108.7 Total Debt $151.0 $164.9 How much of the Principal was paid off for the Mortgage bond from 2021 to 2022