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.

Does anybody see this estimate?