Calculate a date based on text value

Here's one way to do it in the query editor.  To see how it works, just create a blank query, open the Advanced Editor and replace the text there with the M code below. Note that Power Query is case sensitive, so you can wrap in Text.Lower if you expect values of different case.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMtQ31DcyMDJW0lHKyy9RKC1KT80rUYrVAckYwWTSEjOLcipRJY1hkmWpRQipWAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Date Submitted" = _t, Urgency = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date Submitted", type date}, {"Urgency", type text}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Deadline", each if [Urgency] = "not urgent" then Date.AddMonths([Date Submitted], 1) else if [Urgency] = "fairly urgent" then Date.AddDays([Date Submitted], 17) else Date.AddDays([Date Submitted], 7))
in
    #"Added Custom"

Pat