The manufacturing date of the Milk = 31/12/2021
It expires in a week 7 days.
The expiry date of the milk will be 7 days after 31/12/2021.
As 31 December is the last date of December so the next 7 days fall in January. 7th day of January is 07
So the 7th Day of January 2021 is 07/01/2022.