I have the following sum function that requires lots of time to give an output:

```
Sub Sum_multiple_columns()
    Dim ws As Worksheet
    Dim destinationLastRow As Long, i As Long
    Dim TotalCoverage As Double
    Dim rng As Range, MyResultsRng As Range
    Dim cell As Range

    Const FirstCol As Long = 12 ' "L"
    Const LastCol As Long = 24 ' "X"
    Const TotalCoverageColumn As Long = 9
    Set ws = ThisWorkbook.Worksheets("Master")
    destinationLastRow = ws.Range("A" & Rows.Count).End(xlUp).Row
    For i = 5 To destinationLastRow
        Set MyResultsRng = ws.Range("K" & i)
        For Each cell In MyResultsRng
            Set rng = ws.Range(ws.Cells(i, FirstCol), ws.Cells(i, LastCol))
            TotalCoverage = Application.WorksheetFunction.Sum(rng.Value)
            With MyResultsRng
                .Value = TotalCoverage
                .HorizontalAlignment = xlCenter
                .Font.Color = RGB(40, 101, 156)
                .Font.Bold = True
                .Font.Size = 9
                .Font.Name = "Calibri"
                .NumberFormat = "0.00"
             End With
        Next cell
    Next i
End Sub

```

In your opinion, how could I speed up this code which is intented to sum values from column L to X and put the result into column K for every row in the list.

Thank you