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

a$.7$ years at an interest rate of $7\%$ per year.

b$.14$ years at an interest rate of $7\%$ per year.

c$.7$ years at an interest rate of $14\%$ 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$.7$ years at an interest rate of $7\%$ per year.

The future value of $$8,000$ in $7$ years at an interest rate of $7\%$ per year is $

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