ANSWER
It would take 45 good years
EXPLANATION
We calculate simple interest using the formula,
[tex]I=\frac{P\times T\times R}{100}[/tex]
From the question,
[tex]I=324[/tex] dollars
[tex]R=6[/tex]%
and
[tex]P=120[/tex] dollars
We substitute into the above formula
[tex]324=\frac{120\times T\times 6}{100}[/tex]
[tex]324=\frac{720\times T}{100}[/tex]
[tex]324\times100=720\times T[/tex]
[tex]\frac{324\times100}{720}=T[/tex]
[tex]\frac{324\times10}{72}=T[/tex]
[tex]45=T[/tex]
Therefore it would take 45 years.