Expression.Error: Cannot convert the value to type Number

Hi,

I am trying to paramaterize the number of days within date.isinpreviousNdays(datetime,number of days) function. But I am getting following error.

Expression.Error: We cannot convert the value "& DaysPrior &" to type Number.
Details:
Value=& DaysPrior &
Type=Type 

Please find below my entire code:

let
Source = Exchange.Contents(ExchangeEmailID),
Mail1 = Source{[Name="Mail"]}[Data],
#"Filtered Rows1" = Table.SelectRows(Mail1, each Text.StartsWith([Folder Path], "\Inbox\")),
#"Filtered Rows" = Table.SelectRows(#"Filtered Rows1", each Date.IsInPreviousNDays([DateTimeReceived], "& DaysPrior &") or Date.IsInCurrentDay([DateTimeReceived])),
#"Filtered Rows2" = Table.SelectRows(#"Filtered Rows", each Text.StartsWith([Subject], "Cash")),
#"Filtered Rows3" = Table.SelectRows(#"Filtered Rows2", each ([HasAttachments] = true)),
#"Filtered Rows4" = Table.SelectRows(#"Filtered Rows3", each Text.Contains([DisplayTo], "Dennis, Kristy A.") or Text.Contains([DisplayTo], " Matteson, Heather E") or Text.Contains([DisplayTo], "Galentine, Ginnie")),
#"Removed Other Columns" = Table.SelectColumns(#"Filtered Rows4",{"Subject", "Attachments"}),
#"Inserted Text After Delimiter" = Table.AddColumn(#"Removed Other Columns", "Text After Delimiter", each Text.AfterDelimiter([Subject], " "), type text),
#"Renamed Columns" = Table.RenameColumns(#"Inserted Text After Delimiter",{{"Text After Delimiter", "Date"}}),
#"Changed Type" = Table.TransformColumnTypes(#"Renamed Columns",{{"Date", type date}}),
#"Removed Columns" = Table.RemoveColumns(#"Changed Type",{"Subject"}),
#"Added Custom" = Table.AddColumn(#"Removed Columns", "Custom", each [Attachments]{0}[AttachmentContent]),
#"Filtered Hidden Files1" = Table.SelectRows(#"Added Custom", each [Attributes]?[Hidden]? <> true),
#"Invoke Custom Function1" = Table.AddColumn(#"Filtered Hidden Files1", "Transform File from CashBalance (2)", each #"Transform File from CashBalance (2)"([Custom])),
#"Removed Other Columns1" = Table.SelectColumns(#"Invoke Custom Function1",{"Date", "Transform File from CashBalance (2)"}),
#"Expanded Table Column1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File from CashBalance (2)", Table.ColumnNames(#"Transform File from CashBalance (2)"(#"Sample File (2)"))),
#"Changed Type1" = Table.TransformColumnTypes(#"Expanded Table Column1",{{"Portfolio", type text}, {"Cash Balance", Currency.Type}})
in
#"Changed Type1"

Please let me know ASAP how to paramaterize the 90 days within the function.