A particle that carries an unknown amount of charge is placed at the center of a hollow metal sphere of inner radius \(R_{\mathrm{i}}\) and outer radius \(R_{0}\). The magnitude of the electric field outside the sphere at any radial distance \(r\) from the center is \(3 k q / r^{2}\) (with \(q>0\) ) and is directed toward the center. The charge on the inner surface of the sphere is \(-2 q\). What are (a) the charge on the particle and \((b)\) the charge on the sphere?