two things wrong with the sql. You need to add + ' WITH ' + to the second line. And the exec command needs brackets.

Declare @StrSql varchar(1000)

Set @strsql =

'Backup Database' + ' ' + (Select Database_Name From dbo.Db_Backups)

+ ' ' + 'To Disk' + ' ' + '=' + ' ' + (Select Backup_to From dbo.Db_Backups) + ' WITH ' +

+ ' ' + (Select Format From dbo.Db_Backups) + ','

+ ' ' + (Select Init_NoInit From dbo.db_Backups) + ','

+ ' ' + 'Name' + ' ' + '=' + ' ' + (Select Backup_name From dbo.db_Backups) + ','

+ ' ' + (Select Skip_Noskip From dbo.db_backups) + ','

+ ' ' + (Select rewind_Norewind From dbo.db_Backups) + ','

+ ' ' + (Select Nounload_unload From dbo.db_Backups) + ','

+ ' ' + 'Stats =' + ' ' + ' ' + (Select Stat_report From dbo.db_backups)

print @strsql

Exec (@strsql)

GO