Deriving Log-Price Dynamics

Let's say $S_t$ follows the dynamics:

$$dS_t = 3 S_t dt + 4 S_t dW_t$$

where $W_t$ is a standard Brownian motion.

Find the dynamics of $X_t = \ln(S_t)$, where we can write the dynamics as:

$$dX_t = a dt + b dW_t$$

Find $a^2 + b^2$