Adding bath tub drain to 3 inch stack

I've just cracked the concrete to add a new tub drain line in my basement. The stack (3") goes to 45degree angle once below the floor, I'm trying to figure out how to add this and have drawn a basic view on what I have thought might work, and ideas or suggestions are greatly appreciated. Thanks in advance..

I would do a wye branch of that. Looks like thats what you have for the addition. Don't forget the vents you will need for the new plumbing.