From the given information, we know that the decreasing function values is
![V(t)=3600(3^(-0.15t))](https://img.qammunity.org/2023/formulas/mathematics/college/zbvb4zwm9eoy2808g966ebzk7u012v8s5f.png)
and we need to find the time t when V(t) is equal to $1200. Then by substituting this values into the function, we have
![1200=3600(3^(-0.15t))](https://img.qammunity.org/2023/formulas/mathematics/college/j7vlw6ecajm6fv246bnn0v3vcdv1n909hr.png)
By dividing both sides by 3600, we get
![3^(-0.15t)=(1200)/(3600)=(1)/(3)](https://img.qammunity.org/2023/formulas/mathematics/college/t4lgfbwukqkp91hhwiijhtaliavx0rc39p.png)
So we have the equations
![3^(-0.15t)=(1)/(3)](https://img.qammunity.org/2023/formulas/mathematics/college/jg9uk37c6zxdkddu2p9dleymr5lar7pn7v.png)
From the exponents properties, we know that
![3^(-0.15t)=(1)/(3^(0.15t))](https://img.qammunity.org/2023/formulas/mathematics/college/v5vyowweptrwplt86tf53cgdd0d8d3lam6.png)
so we have
![(1)/(3^(0.15t))=(1)/(3)](https://img.qammunity.org/2023/formulas/mathematics/college/vv5owuq6hwummsa9cmn0cidcvem3p4rk0q.png)
or equivalently,
![3^(0.15t)=3](https://img.qammunity.org/2023/formulas/mathematics/college/jhdntc7g8r12tdgcdo4sydwzcp7jtp41sj.png)
This means that
![0.15t=1](https://img.qammunity.org/2023/formulas/mathematics/college/wfgnamkt9b3ofdu9nq7g8ep1gmem1tljb6.png)
Then, by dividing both sides by 0.15, we obtain
![t=(1)/(0.15)=6.6666](https://img.qammunity.org/2023/formulas/mathematics/college/pg9j5ieuhaeah577qth3dyr0b38tnnn2ee.png)
So, by rounding to the nearest hundreadth, the answer is 6.67 years