A parallel-plate capacitor is made from two plates 12.0 cm on each side and 4.50 mm apart. Half of the space between these plates contains only air, but the other half is filled with Plexiglas^®of dielectric constant 3.40 (Fig. P24.72).An 18.0-V battery is connected across the plates. 

(a) What is the capacitance of this combination? 

(b) How much energy is stored in the capacitor? 

(c) If we remove the Plexiglas^® but change nothing else, how much energy will be stored in the capacitor?

Figure P24.72 Plexiglas Air