Rotate parent to aim child in 2D

What I basically have is a character holding a rifle. What I want to achieve is that, given a point in the world, the character's torso rotates in such a way that the rifle is aiming at the given point. I tried using the solutions provided for a similar question (but in 3D) and it didn't work. I tried many approaches but I'm afraid my knowledge of geometry is not deep enough to allow me to solve this issue on my own. Thanks in advance for any help.