Answer: The simple subject of this sentence is "day " and the simple predicate is "ended".
Explanation: The simple subject of a sentence is the thing, person or animal that performs an action or experiences a particular state. Moreover, the simple subject does not include the modifiers. In that way, the simple subject of the sentence provided is "day" ("the longest most boring" and "of his life" work as modifiers). On the other hand, the simple predicate is the main verb in the predicate, which indicates what the subject is doing. The simple predicate in the sentence provided is "ended".
