The backup regimen for a file server is to run a full backup every Sunday and cumulative incremental backups Monday thru Saturday evenings. On Wednesday morning, the server and storage are lost in a c

One tape is insufficient because a full restore requires both the full backup and the cumulative incremental backup containing all changes up to the point of failure.

To restore the server, you need the last full backup performed, which was on Sunday. Additionally, with cumulative incremental backups, you only need the latest cumulative incremental tape to restore all changes since the last full backup. Since Wednesday morning is after Tuesday evening's backup, the Tuesday tape contains all changes from Monday and Tuesday relative to Sunday's full backup, requiring a total of two tapes (Sunday's full and Tuesday's cumulative incremental).

Three tapes would be needed if the regimen was differential incremental (full + Monday + Tuesday) or if you needed more than just the latest cumulative.

Four tapes is incorrect as the cumulative incremental strategy consolidates changes, meaning only the most recent cumulative tape is needed along with the full backup.