Charge q is moving at constant speed v along the positive x-axis. Two other charges -q and 2q are moving at constant speeds v and 2v along positive y and negative z axes, respectively. Assume that at t = 0, q is at the origin, -q is at (0,a,0), and 2q at (0,0,a). Find the Cartesian components of the magnetic field at a point (x,y,z) for t > 0.