Solution
= Solution
{c}
Apply <Itô's formula> to $V_t=A(t)S_t^3$, where $A'(t)=-(2r+3\sigma^2)A(t)$. Since $dS_t/S_t=\mu\,dt+\sigma\,dW_3(t)$, the drift and diffusion are
$$
\frac{dV_t}{V_t}=\bigl(-(2r+3\sigma^2)+3\mu+3\sigma^2\bigr)dt+3\sigma\,dW_3(t).
$$
Thus
$$
\boxed{\overline\mu=3\mu-2r,\qquad\overline\sigma=3\sigma.}
$$
Under the risk-neutral measure its drift becomes $3r-2r=r$, as required for a traded, non-dividend-paying replicating asset.