This can be achieved using an assign instead of three with following steps:
create a variable named No_Of_days as Int64 by selecting browse for types.
In the value use this expression DateDiff(DateInterval.Day,CDate(now.ToString(“MM/dd/yyyy”)),Cdate(DateTime.ParseExact(your_date_String_Var.Trim,“dd/MM/yy”,System.Globalization.CultureInfo.InvariantCulture).ToString(“MM/dd/yyyy”)))