A parallel plate capacitor of capacitance \( 12.5 \, \text{pF} \) is charged by a battery connected between its plates to potential difference of \( 12.0 \, \text{V} \). The battery is now disconnected and a dielectric slab \( (\varepsilon_r = 6) \) is inserted between the plates. The change in its potential energy after inserting the dielectric slab is ____________ \( \times 10^{-12} \, \text{J} \).
