To find the approximation of \( \log_9(1620) \), we can use the change of base formula:
\[ \log_9(1620) = \frac{\log_{10}(1620)}{\log_{10}(9)} \]
First, we calculate \( \log_{10}(1620) \) and \( \log_{10}(9) \):
- \( \log_{10}(1620) \approx 3.209515 \) (using a calculator)
- \( \log_{10}(9) \approx 0.954243 \) (since \( 9 = 3^2 \) and \( \log_{10}(3) \approx 0.477121 \))
Now substitute these into the change of base formula:
\[ \log_9(1620) \approx \frac{3.209515}{0.954243} \approx 3.363417 \]
Rounding to six decimal places, we find that:
\[ \log_9(1620) \approx 3.363417 \]
Thus, the correct answer is:
3.363417