DatePart("w", varDateVariable, vbSaturday) returns a number corresponding to
the day of the week. By specifying vbSaturday as the 3rd argument, it will
return 1 for Saturdays, 2 for Sundays, 3 for Mondays and so on up to 7 for
Fridays.
By subtracting that value from 7, therefore, you know how many days it is
until the next Friday, so you add that many days to your date.