physics - How can I determine the direction of the balls after collision in billiards game?

I'm making a billiard game and I have two questions:

How do I find the velocity of two balls when they collide with each other and how do I apply it to both balls?

I already know the angles that they're gonna move, I just need to find the velocity that they'll move in those directions.

My game is in 3D, and I'm using Unity. I don't want to use Unity's built-in physics to compute the result in this case, I'd like to know how to compute it myself.