Magnetic field in a infinitley long wire

[hitman0097]

Homework Statement

An infinitely long wire lies along the z axis and carries a current of 12 A in the positive z direction. A second infinitely long wire is parallel to the z axis at x = 8.2 cm.

a.)Find the current in the second wire if the magnetic field at x = 1.6 cm is zero.
b.)What is the magnetic field at x = 5 cm?

Homework Equations

F=I(LxB)

The Attempt at a Solution

I am lost with this one.

 

[rl.bhat]

What is the relevant equation for the field due to current carrying infinite long wire?