Hello!
I have an object “hand”, which is a parent of an object “gun”. I need to calculate the rotation angle for the hand so that the muzzle of the gun is pointing at the cursor, but I don’t know how to implement this with a formula. How is it possible to do this? 
How I have it right now:
How I want it to be:
I attach an example:
My Project.zip (45.1 KB)
I have not looked at the attached sample project, but the basics of rotation towards a certain point can be seen in this example:
I think you need to make sure that the point you rotate around is the hand or maybe the center of the gun. Let that point be a game object and position the sprites accordingly.
I added a pivot point to the arm. But I need to rotate my hand to point the muzzle of the gun towards the cursor. I don’t know how to apply the muzzle angle to the arm angle.
Arm pivot point:
Gun muzzle pivot point:
You need to calculate the rotation with respect to the “elbow” position, not the shoulder point.
Since it looks like the lower arm is at a right angle (angle C) to the upper arm, you can use the example that @britzl gave, calculate the angle for the shoulder (angle A) and use Pythagoras to calculate angle B.
