Question 121

Hey Leon, 

For Q121, the hint for WOW calculation reads  as the following

• Definition of WoW change:  (number of today's first-ever bookings  - the same day of last week's first-ever bookings ) * 100.0 / today's first-ever bookings.

The code in the solution however is divided by the value of 7 days prior. 

(first_bookings -  LAG(first_bookings, 7) OVER(order by date))  * 100.0/ (LAG(first_bookings, 7) OVER(order by date)) AS wow_change

Is this correct? If yes, why are we taking the 7 days prior value as today's first-ever booking?