FIFO Cost Valuation for The sales transactions

FYI

let
    Source = Excel.CurrentWorkbook(){[Name="Table15"]}[Content],
    #"Change Type" = Table.TransformColumnTypes(Source,{{"Total Value", type number}, {"value per unit", type number}}),
    Custom1 = 
        Table.Group(
            #"Change Type",
            "Symbol",
            {
                "q",
                each
                    let
                        t = Table.Group( _, "type", { "w", (x)=> x } ),
                        buy = t{0}[w],
                        sale = t{1}[w],
                        f = 
                            (p)=>
                            List.Accumulate(
                                Table.ToRows( buy ),
                                { 0, 0 },
                                (x,y)=>
                                    if x{1} + y{1} < p
                                    then { x{0} + y{1} * y{4}, x{1} + y{1} }
                                    else { x{0} + List.Max( { p - x{1}, 0 } ) * y{4}, x{1} + y{1} }
                            ){0},
                        a =
                            Table.AddIndexColumn( sale, "i", 1, 1 ),
                        b =
                            Table.AddColumn( a, "q", (x)=> f( List.Sum( Table.FirstN( a, x[i] )[Units] ) ) ),
                        c =
                            Table.AddColumn( b, "cost", (x)=> if x[i] = 1 then x[q] else x[q] - b[q]{x[i]-2} ),
                        d =
                            Table.AddColumn( buy, "cost", (x)=> null ) & Table.RemoveColumns( c, { "i", "q" } )
                    in
                        Table.Sort( d, "index" )
            }
        )[q],
   Custom2 = 
        Table.Combine( Custom1 )
in
    Custom2