A direct answer to your question is
let
Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
SumUpSales = Table.AddColumn(Source, "Sales of insured devices", each if List.Contains({"iPhone","iPad","iPod"}, _[Platform]) and Text.Upper(_[Insured]) = "Y" then _[#"Mobile sales $"] else null, type number)
in
SumUpSales
However, I would like to stress you few things.
First, it's better to convert values in [Insured] column to boolean first. That way you can catch errors before they corrupt your data without you noticing. My example doesn't do that, all it does is negating letter case in [Insured], since PowerM is case-sensitive language.
Second, you'd better use null rather than text value error. Then, you can set column type, and do some math with its values, such as summing them up. In case of mixed text and number values you will get an error in this and many other cases.
And last.
It is probably better way to use a pivot table for visualizing data like this. You just need to add a column which groups all Apple (and/or other) devices together based on the same logic, but excluding [Insured]. Pivot tables are more flexible, and I personally like them very much.
