Designing a simple magnetic field gen with a straight wire. Need current density

[ARBY1]

Homework Statement

Need to design a simple magnetic field generator of radius a= 2mm. The solid metal wire must carry a current density, jw, uniformly distributed over its cross section. The current density that must be found must have a magnetic field at a radial distance of r= 8mm from the axis of the wire is 7.5 10^-13 Tesla. Ignore end effects. Must develop the equation using Ampere's Law as the beginning derivation.

Homework Equations

I=∫J*da
A=r*r*∏
B∫J*ds

The Attempt at a Solution

I am have been trying to start off this by drawing a diagram but I don't even think it is correct.

http://imageshack.us/photo/my-images/440/finalprep.png/

 

[ARBY1]

Also I forgot an equation jw inside is

J=(I)/(∏*r*r)