The energy flux (or intensity) of plane electromagnetic wave is equal to the time averaged magnitude of the Poynting vector,
I = (ε₀∙c/2)∙ E₀² = (µ₀∙c/2)∙ B₀²
where
ε₀ vacuum permittivity, c speed of light, E₀ amplitude ot the electric field, µ₀∙magnetic constant , B₀ amplitude of the magnetic field
For this wave
I = <S> = (µ₀∙c/2)∙ B₀²
= (4π×10⁻⁷Tm/A ∙ 2.998×10⁸m/s / 2)∙ (1.2×10⁻¹⁰ T)²
= 5.425×10⁻¹⁸J/m²s
Multiply this by the area and the time and you have the energy you are looking for:
E = I ∙ A ∙t
= 5.425×10⁻¹⁸J/m²s ∙ 0.2m² ∙ 50s
= 5.425×10⁻¹⁷J
