homework and exercises - Capacitance of spherical capacitor when earthed

The capacitance of a spherical capacitor is given by

$$C=\frac{4\pi \varepsilon_{0}}{\left ( \frac{1}{a}-\frac{1}{b} \right )}$$

How can I find out the capacitance of the capacitor when

1. The inner sphere is earthed.



2. The outer hollow sphere is earthed.