Having problem to convert a range to a number format

Hi. I'm trying to convert a range (a1:a12 in the sample) to a number format, but the code below does nothing.

Know this tiny green sign appears on a cell when there is an error? It suggested me to convert the cell to a number, but when I tried to record this move in order to check its code, it produced basicallty an empty code.. weird, isn't it?

Dim b As Range, c As Double
Set b = Worksheets("dirot").Range("a40:a51")
b.Select
b.NumberFormat = "0"
c = Application.Max(b)
MsgBox c