What is the simple predicate in the sentence "the package in the brown box was by far the heaviest."

"was by far the heaviest."

Explanation:

The predicate consists of a statement about the subject in a sentence, and it usually comes after the verb - which in this case is the to-be verb was.

The subject of the sentence is "The package in the brown box" (The object that's being talked about, along with its description).

The predicate of the sentence states something about this package (its weight compared with other objects).