This funtion returns a number representing the nth day of a week, based on a date.
Where date: can be either represented as a numerical or string expression.
And first_day_of_week: Is a constant that will represent the first day of the week.
The possible value of "first_day_of_week":
vbUseSystem 0 Use the National Language Support API setting.
vbSunday 1 Sunday (if constant is omitted, value used by default)
vbMonday 2 Monday
vbTuesday 3 Tuesday
vbWednesday 4 Wednesday
vbThursday 5 Thursday
vbFriday 6 Friday
vbSaturday 7 Saturday