How to find a general sum formula for the series: 5+55+555…

55 fiveSpecialties: The Five 55 is a nehborhood sports cocktail bar focused on local craft beers, hand-made drinks and delicious modern American food in an upscaleHotel 55 is a modern and refined 4-star superior hotel housed in the interior of a nineteenth-century noble palace completely restored in the heart of the historic center of Rome, in Via