* Subject: "Boxes sweaters" (This is a compound subject, acting as a single unit)
* Complete Verb: "were delivered" (This is a passive voice verb. "Were" is the helping verb, and "delivered" is the main verb.)
The sentence is a bit awkward, and it's missing a prepositional phrase to make it complete. It would be clearer as: "Sixty boxes of sweaters were delivered to the store before the big sale."