Passing Variable To String Compare In Function

I have created a function with:

set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
GO

ALTER FUNCTION [dbo].[fn_concat_boxes](@item varchar, @week int)
RETURNS VARCHAR(100)
AS
BEGIN

DECLARE @Output varchar(100)

SELECT @Output = COALESCE(@Output + '/', '') +
CAST(quantity AS varchar(5))
FROM flexing_stock_transactions
WHERE item = @item AND week = @week
GROUP BY quantity
ORDER BY quantity

RETURN @Output


END

how can I pass the variable @item correctly for the string comparison

WHERE item = @item AND week = @week

to work correctly please?

WHERE item = '@item' AND week = @week

won't work and

WHERE item = @item AND week = @week

won't work.