Wave Equation Word Problem

At time , two explosions occur in 3-space. They are contained within the spheres of radius 1 at the points (4,0,0) and (0,9,0). If you are located at hte point (0,5,0), what is the largest set of times for which you will not hear sounds from either explosion?

OK, so this is a 3-D wave problem, I know that, and I could probably solve it pretty easily. However, I'm having trouble with the setup. Can someone point me im the right direction as far as the setup is concerned?