Two long parallel wires $40.$ cm apart are carrying currents of $10.$ A and $20.$ A in the same direction. What is the magnitude of the magnetic field halfway between the wires?

Group of answer choices

$3\mathrm{.}0$ x $10-5$ T

$1\mathrm{.}0$ x $10-5$ T

$2\mathrm{.}0$ x $10-5$ T

$4\mathrm{.}0$ x $10-5$ T