A bond has a maturity of 12 years, duration of 9.5 years at a promised yield rate

Question:

A bond has a maturity of 12 years, duration of 9.5 years at a promised yield rate of 8%. What is the bond's modified duration?

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...