count occurences of multiple values

Hello community, 

I struggle with the following request:

I count the occurence of a certain value (here 50) in multiple columns with this query

let
    source = 
    #table(
        {"Width A", "Width B", "Width C"},
        {{50, 50, 50}, {40, 50, 50}, {40, 40, 40}, {45, 40, 40}}
    ),
    #"Changed Type" = Table.TransformColumnTypes(source,{{"Width A", Int64.Type}, {"Width B", Int64.Type}, {"Width C", Int64.Type}}),
    #"Count 50&45" = Table.AddColumn(#"Changed Type", "Count", each 
        List.Count(
            List.Select(
                Record.ToList(
                    Record.SelectFields(_, {"Width A", "Width B", "Width C"})
                ), each _ = 50 
            )
        )
    )
in
    #"Count 50&45"

 this shall now also count the number 45, so that the fourth row in the example returns 1

How can I achieve this? It sounds so simple, but I can't figure it out... 

thanks a lot in advance