Solution to Excel BI Excel/Power Query Challenge 19

gistfile

let
  Source=Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    CustomColumn = Table.AddColumn(Source, "Answer", each let
          Spl=Text.Split([Sentence]," "),
          lenSpl=List.Transform(Spl,each Text.Length(_)),
          addlen=List.Zip({Spl,lenSpl}),
          tbl=#table({"Sentence","length"},addlen),
          filter=Table.SelectRows(tbl,
              let max = List.Max(tbl[length]) 
              in each 
                  [length] = max)[[Sentence]][Sentence],
          combine=Text.Combine(filter,", "),
          proper=Text.Proper(combine)
      in proper)
in
    CustomColumn