Field in a coaxial cable

A coaxial cable has an inner conductor of radius $0.50\mathrm{mm}$ and an outer conductor with radii $3.0\mathrm{mm}$ and $3.5\mathrm{mm}$; the two conductors carry the current $10\mathrm{A}$ in opposite senses. Compute the magnitude of the magnetic field at $1.0\mathrm{mm}$ and at $4.0\mathrm{mm}$ from the axis.