Frequency = 1 / (2π√LC)
Frequency = 1 / (2π · 2.8 x 10⁻⁴ · C)
Frequency = 1 / (1.759 x 10⁻³ · C)
Frequency = (568.4 / C) Hz.
Energy stored in a capacitor = 1/2 C V²
Energy = 1/2 C · 2.25 x 10⁴
Energy = (11,250 · C) Joules
Neither of the answers can be completely specified without knowing the value of the capacitor.