A spherical capacitor is formed from two concentric, spherical, conducting shells separated by vacuum. The inner sphere

Question:

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