Change the italicized words and combine the sentence with an adjectival infinitive. This book is excellent. You should read it.
Change the italicized words and combine the sentence by using a prepositional phrase.
Our town has a library. I go there every week.
Grammar is a lot of fun, as you get the hang of it. In the first sentence, your teacher is asking you to combine the sentences by using an adjectival infinitive. Not easy. Here it is:
"This is an excellent book to read." In this sentence, "to read" is an infinitive and it is used adjectively. Think of it this way: which book are you talking about? You're talking about the one that is "excellent to read." Clearly an adjective.
Here is the second sentence: "I go every week to the library in my town." "To the library" and "in my town" are prepositional phrases. This sentence is one possibility. If you want to rewrite the sentence with only one prepositional phrase, you can combine town and library. The new sentence would read: "I go every week to my town library."
The meaning is the same, but "town" is now modifying "library."
There are other possibilities, but the two answers I have given are the most succinct way to combine the sentences.
If you want more grammar help, take a look at the link below.