Load bearing header calculation

Need to calculate a header. This is a header on 2nd floor opening on a load bearing wall. Under it, is 1st floor, and crawl space. This load bearing wall is on top of a beam on 1st floor, with a loaded width of 15ft. There is already a header of 3"x5" under the floor joists of 3rd floor. Then there is the load bearing wall, with a top plate of 3"x3". On top of this load bearing wall, is a 3rd floor load bearing wall, with a loaded width of 10ft. On top of this, is the 4th floor load bearing wall, with a loaded width of 8ft. On top of that, is the flat roof. See the sketch attached. I need to open up 5'4" in the wall on 2nd floor. I want to integrate the required header with the existing 3"x3" top plate and/or the 3"x5" beam on top of the top plate. Ideally, I could make a flitch plate in place, using the 3"x3" and/or 3"5. The flitch plate can be made by 3 layers: 1/2"steel - 3"x3" top plate - 1/2" steel. If needed, the thickness of the steel can increas etc. No need for any drawings. Just need the sizes of mateirials.