Answer:
about 11 years
Step-by-step explanation:
we know that
The simple interest formula is equal to
[tex]A=P(1+rt)[/tex]
where
A is the Final Investment Value
P is the Principal amount of money to be invested
r is the rate of interest
t is Number of Time Periods
in this problem we have
[tex]t=?\ years\\ P=\$4,000\\ A=\$8,000\\r=9\%=9/100=0.09[/tex]
substitute in the formula above
[tex]8,000=4,000(1+0.09t)[/tex]
solve for r
[tex]2=(1+0.09t)[/tex]
[tex]0.09t=2-1[/tex]
[tex]0.09t=1[/tex]
[tex]t=11.1\ years[/tex]
