Estimate

Hi! I want to show the following: Let $u \in \, C^2(\mathbb{R}^3 \times (0,\infty))$ solve:
$u_{tt}-\triangle u=0$ on $\mathbb{R}^3 \times (0,\infty)$
$u=g, \, u_t=h$ on $\mathbb{R}^3 \times \{t=0\}$ with $g, h$ having compact support. Then there exists $C>0$, so that $|u(x,t)|\leq \frac{C}{t}$.
I know that a solution is given by $u(x,t)=\frac{1}{4 \pi t^2} \int_{\partial B(x,t)}^{} th(y)+g(y)+Dg(y) \cdot (y-x) dS(y)$, with $\partial B(x,t)$ meaning the boundary of the ball around $x$ with radius $t$.