Answer:
6.93 years
Step-by-step explanation:
For computing the number of years we use the NPER formula i.e to be shown in the attachment 
Given that
Present value = $8,000
Future value = $0
Rate of interest = 9%
PMT = $1,600
The formula is shown below: 
= NPER(Rate;PMT;-PV;FV;type) 
The present value come in negative 
So, after applying the above formula, the number of years is 6.93 years