A spherical capacitor is formed from two concentric, spherical, conducting shells separated by vacuum. The inner sphere has radius 15.0 $\mathrm{cm}$ and the capacitance is 116 $\mathrm{pF}$ (a) What is the radius of the outer sphere? (b) If the potential difference between the two spheres is $220 \mathrm{V},$ what is the magnitude of charge on each sphere?