Displacement current is given by id=dtϵ0dϕE
Or id=dtϵ0d(EA), where E=Aϵ0q
Or id=ϵ0dtd(Aϵ0qA)=dtdq=dtd(CV)
Or id=CdtdV=dϵ0AdtdV
Putting the values, we have
4.425×10−6=d8.85×10−12×40×10−4×106
d=2×10−6×10−4×106×40
d=80×10−4=8×10−3m
Hence, value of x=8.