Given vectors $a=(2,3)$ and $b=(-1,5)$ :

$($a$)$ Find $a+b,a-b,$ and $3a-5b.$

$($b$)$ Find the angle that a makes relative to the $x-$axis. $($Answer may be left in radians.$)$

$($c$)$ Find an exact unit vector in the direction of $3a-5b.$

Solve using Python, please and thank you.