From Faraday's Law, the emf, ε , induced around a single loop of conductor is proportional to the rate of change of the magnetic flux, Φ, through the area, A , of the loop.
ε = -N . (ΔΦ / Δt)
ε = -50 . (-30 - 30) / 0.42
Therefore Induced voltage = ε = 7143 V