Calculating turret angle 2D, C++

So I'm trying to figure out how I would get the turret on my little space ship to figure out what angle it is at relative to the world and rotate to point to a target

Both the turret and ship have a relative coord and rotation, the ship's coord and rotation are relative to the world and the turret's are relative to its parent(may not be the body of the ship, might be the wing or such)

All parts calculate a local and global 3x3 transformation matrix if that helps