Which sentence uses correct punctuation?

we walked through the red oak nature center today; it was surprising how many bicyclists were there.
the play was an actual wedding party, the actors were funny, outgoing, and playful party guests who interacted with the audience.
it was an extremely hot day, 99 degrees with a heat index of over 100 degrees.
we never found the answer to our question, in fact, we’re still looking to this day.

The answer to your question would be that the sentence that uses correct punctuation would be the following one: We walked through the Red Oak Nature Center today; it was surprising how many bicyclists were there.

This sentence is an example of the correct use of the semicolon. Its most common use is to join two independent clauses without using a conjunction like and.

Two circuits are called circuit A and Circuit B. The equivalent resistance of Circuit A is x and that of Circuit B is y between 1 and 2.