Note: For the problems without a coordinate system, feel free to define your own coordinate system to help you solve the problem.

Two infinitely long, parallel wires are carrying $20$ A currents in opposite directions. Determine the magnetic flux density $B$ at point P in Figure $1.$

Hint: the magnetic flux density due to one infinite long wire with current I flowing along positive $z$ axis is $B=$hat$()\frac{{}_0\text{I}}{2r},$ where $r$ is the radial distance from the wire.

Figure $1$: problem $1.$