I am confused on this physics question

Question

bolt of lightning, such as the one shown on the left side of the figure below, behaves like a vertical wire conducting current. As a result, it produces a magnetic field whose strength varies with the distance from the lightning. A 83 turn circular coil is oriented perpendicular to the magnetic field, as shown on the right side of the figure below. The coil has a radius of 0.833 m. If the magnetic field at the coil drops from 4.72 ✕ 10-3 T to 0.00 T in 10.5 µs, what is the average emf induced in the coil?

Answer 1

Without the picture to look at, it is hard to answer the question.  But if I am interpreting the information correctly, then

 

E = -N(dΦ/dt) = -NA(dB/dt)

 

N = number of turns in the coil = 83

A = cross sectional area of the coil

 

A = πr² = π(0.833 m)²

 

dB/dt = ΔB/Δt = (-4.72 x 10^-3 T)/(10.5 x 10^-6 s)

 

Plug in the numbers and get E in volts.