Exercise using "acabar de"

Exercise using "acabar de"
 

The instructions for this set of sentences are as follows: "Rewrite the following sentences using acabar de in the present or in the imperfect."

My questions are as follows:

3. Given sentence: Lo hemos decidido justo en este momento.
Answer given by the book: Lo acabamos de decidir.
My question: Why wouldn't you keep the "haber"? To me it seems to change meaning. I wrote "Lo acabamos de haber decidido." To me, it seems like the difference between "we just decided" and "we have just decided". Minor difference, I know, but a difference nonetheless...

4. Given sentence: Juan habló con Antonio justo cuando se encontró conmigo.
Answer given by the book: Juan acababa de hablar con Antonio cuando se encontró conmigo.
My question: I don't understand the meaning of either sentence.....

6. Given sentence: Les he llamado hace un minuto.
Answer given by the book: Les acabo de llamar.
My question: I wrote "acabo de llamarles". Is it the same?

7. Given sentence: Felipe me dijo en ese preciso momento que no me quedara con los libros.
Answer given by the book: Felipe me acababa de decir que no me quedan con los libros.
My question: First question, same as #6, could I write "Felipe acababa de decirme..."? Also, I'm fuzzy on the meaning. Does it mean something like "Felipe just told me that he isn't leaving the books with me"?

Thank you for any help you can give me!!

For number 6 I believe what you have is correct as well.
Same goes for number 7...and I would translate it similarly.

I am in NO way an expert...sorry if i have not helped!!

As a general comment:

The use of the present tense of acabar indicates a closer proximity with the past that the perfect does.

María acaba de marcharse María has just left (moments ago)
María se ha marchado María has left (sometime earlier)

For a past construction, you use acabar in the imperfect.

Acabábamos de sentarnos a la mesa We had just sat down at the table.

Does that help?

Edit: Cross-posting, sorry.

In sentence number 4, the meaning is 'John had just finished speaking with Antonio when he met with me'.

Unless it was mistyped, the book's answer for number 7 isn't right. It should be '... que no me quedara con los libros'.
The meaning of the sentence is 'Phillip told me in that precise moment that I should not keep/take the books'.

Your answer for number six is fine.

I agree with Rusty. The sentence is saying you must give the books back, and the correct tense is: "...que no me quedara con los libros", not "quedan".
"Felipe acababa de decirme que no me quedara con los libros" is a fine answer.

The last one can it be written as "Felipe me acababa de decir que no me quede con los libros" ?

The periphrasis is "acabar de + infinitive" meaning that "infinitive" ended just a second ago. "Infinitivo compuesto" keep the perfective aspect, that is, the action is 100% completed, or in Spain, the action can be also recent. That is what "acabar de" means, so it's unnecessary and confusing because it'd suggested it is recently done yet forgotten (it's done and we're done with it).
The given sentence makes no sense. The only meaningful sentence is the answer: Juan had just spoken with Antonio (or he was coming back from the place where such a conversation took place) when he came across me.
Yes
Given sentence and answer are pretty unrelated and the answer makes little sense without complementary information. To make sense of it

10:00 ---> Sonaba el reloj y Felipe me dijo en ese preciso momento que no me quedara con los libros.
10:05 ---> Felipe me acababa de decir que no me quedara con los libros cuando cambió de opinión y me dijo que me los llevara.

Thanks for all of your helpful answers. I'm finding I understand more than I realized. :) Rusty, yes - it was definitely mis-typed. THANKS! :)