Calculate the Reluctance of a 4-Meter Long Toroidal Coil Made

Calculate the reluctance of a 4-meter long toroidal coil made of low-carbon steel with an inner radius of 1.75 cm and an outer radius of 2.25 cm. The permeability of the steel is 2 × 10-4 Wb/At - m.

A) 2.29 × 106 At/Wb
B) 4.03 × 105 At/Wb
C) 1.96 × 10-5 At/Wb
D) 31.9 × 106 At/Wb