simple subject: class
simple predicate: laughed
simple subject: day
simple predicate: ended
Simple subject is the noun/pronoun that the sentence is talking about.
It does not include any of the adjectives modifying the subject.
Simple predicate is the specific action/verb that the subject did.
Simple predicate may be a verb phrase (main verb with auxiliary verb).
It does not include adverbs or other modifiers for the verb.