You should summarize the most important parts of the book like theme, symbols, and anything else that is a main contribution to the plot. Also, write about your interpretation of the book and what it's message meant in your mind.
The type of sentence given is a compound sentence. It is a compound sentence because it consists of two independent sentences: "I already said yes to someone else" and "I can't go to the dance with you". In order to link the two sentences, the conjunction "because" is used.
Thank you you too may god bless you❤️❤️