$.$ Two long, parallel wires separated by $2\mathrm{.}65$ cm carry currents in opposite directions. The current in one wire is $1\mathrm{.}30$ A$,$ and the current in the other is $3\mathrm{.}00$ A$.$

$($a$)$ Find the magnitude of the force per unit length that one wire exerts on the other. $($n$/$m$)$

$($b$)$ Is the force attractive or repulsive?