When a company redeems bonds from an individual series of serial bonds prior to the maturity date

Question:

When a company redeems bonds from an individual series of serial bonds prior to the maturity date how does it determine the amount unamortized discount or premium to be eliminated under the bond outstanding method?

Maturity
Maturity is the date on which the life of a transaction or financial instrument ends, after which it must either be renewed, or it will cease to exist. The term is commonly used for deposits, foreign exchange spot, and forward transactions, interest...