An object is made of glass and has the shape of a cube 0.12 m on a side, according to an observer at rest relative to it. However, an observer moving at high speed parallel to one of the object's edges and knowing that the object's mass is 2.8 kg determines its density to be 8800 kg/m3, which is much greater than the density of glass. What is the moving observer's speed (in units of c) relative to the cube?