I'm not ready to give you the full program, but basic idea is that you should use trigonometry. Take two planes: one vertical and one horizontal, then run calculations for both. In each one, imagine that there's a right triangle where turret is in one of its non-right vertices and entity is in another with right angle being on line where turret looks in neutral position. You find its legs by subtracting coordinates, then divide one leg by another and take arctan to find desired angle. Here's a demonstration of what I'm talking about: https://www.geogebra.org/classic/kb75gnfv.
