Three spheres each of unit radius have centers P,Q,R with the property that the center of each sphere lies on the surface of the other two spheres. Let C denote the cylinder with cross-section PQR (the triangular lamina with vertices P,Q,R) and axis perpendicular to PQR. Let M denote the space which is common to the three spheres and the cylinder C, and suppose the mass density of M at a given point is the distance of the point from PQR. Determine the mass of M. geometry3D geometrysphere