SQL regular backup and delete expired backup

A -- Full backup
Declare   @ Filename   Varchar ( 100 )
Set   @ Filename = ' D: \ data backup \ '   +   Convert ( Varchar ( 10 ), Getdate (), 120 ) +   ' . Bak '
Backup   Database Coaltraffic To   Disk = @ Filename  
With Init

B

-- Differential backup (must be the same as the full backup)
Declare   @ Filename   Varchar ( 100 )
Set   @ Filename = ' D: \ data backup \ '   +   Convert ( Varchar ( 10 ), Getdate (), 120 ) +   ' . Bak '
Backup   Database Coaltraffic To   Disk = @ Filename  
With Differential

C--Delete files created at @ createdate and of the Bak type

-- It has nothing to do with the Bak file name
Declare   @ Createdate   Datetime
Select   @ Createdate = Getdate () - 1
Execute Master. DBO. xp_delete_file 0 , N ' D: \ data backup \ ' , N ' Bak ' , @ Createdate