The relation between the magnetic flux and the self-inductance of the coil is given by, ϕ=NLI
Now, given that,
Number of turns N=400
Self-inductance L=10mH=10×10−3H
Current, I=2mA=2×10−3A
So, the total magnetic flux is given by, ϕ=400(10×10−3)×2×10−3 ⇒ϕ=8×10−3Wb