The maximum acceleration in SHM is given by \( a_{\text{max}} = \omega^2 A \), where \( \omega \) is the angular frequency and \( A \) is the amplitude.
From the given equation, the angular frequency \( \omega = 3 \, \text{rad/s} \) and the amplitude \( A = 0.6 \).
Thus, the maximum acceleration is:
\[
a_{\text{max}} = (3)^2 \times 0.6 = 18 \, \text{m/s}^2
\]
Therefore, the maximum acceleration is 18 m/s².