This post shows a how to get the week of the year using C#.
This task is not very tough but it will take you something to find the correct answer.
The day variable below will capture the week of day.
DateTime dte = DateTime.Parse(“2018-04-03”);
int day = CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(dte, CalendarWeekRule.FirstDay, DayOfWeek.Monday);