What does the WEEKNUM function do$?$

a$.$

Given a range of cells that contain dates, the function will show which weeks the range covers in a calendar year.

b$.$

Given a specific date, the function will show which week of the month the date falls in from week $1$ to $5.$

c$.$

The function will show, for any given date, how many days are left till the end of the week.

d$.$

The function will show a serial number associated with the week number of a calendar year.