Need help with a table join and or calculation

This can be done in PQ very easily.

See the working here - Open a blank query - Home - Advanced Editor - Remove everything from there and paste the below code to test

TableA

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45W8krMK00sqlTSUfJxBBKGpmZmSrE6yOIeIRFA0sjI0BhNIjjEB0iaQzW4pSYVoZhkaWiCLgE1ytLAEF0GYpahsYElWMY3sSg5A2aSsbG5MYooxBhDcyNzFGGoGRYmQDNiAQ==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Month = _t, Location = _t, Downtime = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Month", type text}, {"Location", type text}, {"Downtime", Int64.Type}}),
    #"Merged Queries" = Table.NestedJoin(#"Changed Type", {"Month", "Location"}, TableB, {"Month", "Location"}, "TableB", JoinKind.LeftOuter),
    #"Expanded TableB" = Table.ExpandTableColumn(#"Merged Queries", "TableB", {"ScheduledTime"}, {"ScheduledTime"}),
    #"Added Custom" = Table.AddColumn(#"Expanded TableB", "Value", each [Downtime]/[ScheduledTime]/60),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"Downtime", "ScheduledTime"}),
    #"Pivoted Column" = Table.Pivot(#"Removed Columns", List.Distinct(#"Removed Columns"[Month]), "Month", "Value", List.Sum)
in
    #"Pivoted Column"

 In case, you need - Code for TableB

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45W8krMK00sqlTSUfJxBBJGhsaWSrE6yOIeIRFA0tjMBF0iOMQHJGFsYgyWcEtNKkIxysjCAl0CapahsRG6DMQwIzMjiIxvYlFyBtwkCzNDFFGoMSYm5ijCUAcZmgEdFAsA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Month = _t, Location = _t, ScheduledTime = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Month", type text}, {"Location", type text}, {"ScheduledTime", Int64.Type}})
in
    #"Changed Type"