A long straight wire of circular cross section of radius a carries a steady current I........................

These are the options for the question :A long straight wire of circular cross section of radius a carries a steady current I. The current is uniformly distributed across its cross section. The ratio of the magnitudes of magnetic field at a point distant a/2 above the surface of wire to that at a point distant a/2 below its surface is

(i) 4 :1 (ii) 1:1 (iii) 4: 3 (iv) 3 :4

The correct answer is -(iii) 4:3