Magnetic Effects of Current and Magnetism Part 2

A rod with circular cross-section area 2cm2 and length 40‌cm is wound uniformly with 400 turns of an insulated wire. If a current of 0.4A flows in the wire windings, the total magnetic flux produced inside windings is 4π×10−6‌Wb. The relative permeability of the rod is
(Given : Permeability of vacuum
µ0=4π×10−7NA−2‌ ) ‌