Composition of Maclaurin Series

Let $f$ be a function with a Maclaurin series given by $2x + \displaystyle\frac{1}{2}x^2 + \displaystyle\frac{1}{3}x^3 + \displaystyle\frac{1}{4}x^4 + \cdots$. The series converges to $f(x)$ for all real numbers $x$. If $g(x) = \sinh(f(x))$, what is the coefficient of $x^3$ in the Maclaurin series for $g$?