Reply in respect of Notice of Defective Return

Notice of defective return u/s 139(9) dated 07/12/2019 has been received

(A) on 07/12/2019 thru the mail

(B) the hard copy of the notice received on 12/12/2019.

There is a time limit of reply in respect of Notice of defective return u/s 139(9) within 15 days from receipt of such notice.

From which date the above 15 days should be counted whether 07/12/2019 or 12/12/2019?

What will be the last date of reply in respect of such notice?