M = μ0 n1 n2 A2
= 4 π × 10−7 × 15 × 10 × 10 × 4 × 10−4
= 4π × 6 × 10−7
= 24 × 3.41 × 10−7
= 75.36 × 10−7
= 7.54 × 10−6 H
= 7.54 μH.