Thank you for reporting, we will resolve it shortly
Q.
Magnetic field B on the axis of a circular coil and far away distance x from the centre of the coil
are related as :
Solution:
Magnetic field on the axis of circular coil is $4\, \pi (R^2 + x^2)^{3/2}$
where R is the radius of the coil and x is the distance of the observation point. At the far away point $x$ > > $R$, so $R^2$ may be neglected as compared to $x^2$. Hence magnetic field is related to x as $B\,\propto\,x^{-3}$