Final answer:
A simple sentence has one idea expressed in a single main clause. The given sentence is a compound sentence because it has two independent clauses connected by the conjunction 'so'.
Step-by-step explanation:
A simple sentence has one idea expressed in a single main clause (also known as an independent clause). A main clause contains a subject and a predicate and can stand alone as a sentence. A simple sentence can be short or long, as shown in the examples below. The phrases in the long sentence add information, but the sentence remains a simple sentence nonetheless because it has only one clause.
The coronavirus spread around in the world in 2020.
School-age children and college students were pushed into virtual learning environments in March 2020, with schools closing for unspecified lengths of time.
A compound sentence has two or more independent clauses. These clauses can be connected by coordinating conjunctions (such as 'and', 'but', 'or'), conjunctive adverbs (such as 'however', 'therefore', 'meanwhile'), or semicolons. In the given sentence, 'It's Jayda's birthday' and 'we should make her a chocolate cake' are two independent clauses connected by the conjunction 'so'. Therefore, the given sentence is a compound sentence.