Point \(\mathrm{P}\) is a distance \(d_{1}=4.0 \mathrm{~mm}\) above a large sheet of metal that carries a current of \(40 \mathrm{~A}\) in the positive \(x\) direction and a distance \(d_{2}=3.0 \mathrm{~mm}\) below a very long wire that carries a current of \(0.35 \mathrm{~A}\) in the positive \(x\) direction. If the magnetic field magnitude at \(\mathrm{P}\) is zero, calculate the width of the metal sheet.