Here are the answers to your questions:
Question 1 A) The revised passage that clears up unclear antecedents is:
Response: Enrico had to work from home and take care of his two-year-old son. They walked over to the park, and while there, Enrico planned to make a call to his co-worker Paul. Enrico, helping his son on the playground slide, talked to Paul using a hands-free headset.
Question 3 A) The correct sentence combining the two sentences by replacing the first sentence with a prepositional phrase is:
Response: The new program on the radio featured live performances by local musicians.
Question 5 A) The sentence that correctly uses a relative pronoun to combine the sentences is:
Response: Leslie set a goal, which is to become a math teacher, and began working toward it.
Feel free to ask if you have more questions!