public static DateTime CreatePreviousDayByWeek(DateTime dt, DayOfWeek dayOfWeek) => DateTimeCalc.OffsetByWeekBefore(dt, dayOfWeek);
public static DateTime CreatePreviousDayByWeek(int year, int month, int day, DayOfWeek dayOfWeek) => DateTimeCalc.OffsetByWeekBefore(Create(year, month, day), dayOfWeek);