Frobenius & Special Functions · Easy problem

The Frobenius solution of Bessel's equation of order $0$ is $J_0(x) = \displaystyle\sum_{k\ge0}\frac{(-1)^k}{(k!)^2}\left(\frac{x}{2}\right)^{2k}$. Find the coefficient of $x^4$ in this series. Express your answer as a common fraction.