Calculate the future value of $$8,000$ in

a$.9$ years at an interest rate of $9\%$ per year.

b$.18$ years at an interest rate of $9\%$ per year.

c$.9$ years at an interest rate of $18\%$ per year.

d$.$ Why is the amount of interest earned in part $($a$)$ less than half the amount of interest earned in part $($b$)?$

a$.9$ years at an interest rate of $9\%$ per year.

The future value of $$8,000$ in $9$ years at an interest rate of $9\%$ per year is $

$($Round to the nearest cent.$)$