Weekly backups of the system are done on Sundays, and daily backups are done the rest of the week. Which of following backup methods were used if the system crashes on Friday and only requires two…

Snapshots are point-in-time images, often used for virtualization, but not typically referred to as a "backup method" in this context alongside incremental.

A full backup strategy on Sunday means all data is backed up. Differential backups then only capture changes made since the last full backup. If the system crashes on Friday, recovery requires the initial full backup from Sunday and only the latest differential backup (from Thursday or Friday morning, depending on timing) to restore all data up to the crash point. This fulfills the "two backup sets" requirement.

If full and incremental backups were used, recovery on Friday would require the full backup from Sunday plus every incremental backup taken since Monday, which is more than two backup sets.

A combination of differential and incremental would still require the initial full backup and multiple incremental backups, making it unlikely to be completed with only two backup sets.