6.1 Replace the expressions in BOLD by pronouns using the word order without “to or for”.
e.g. John gave the book to Henry, becomes John gave HIM the book.
NOTE. The usual order is VERB + PERSON + THING (e.g. show Mary the book), but to give more emphasis to the person we can put it AFTER the direct object and add the prepositions to or for (e.g. show the book to Mary).
REVISION: subject pronoun, object pronoun, possessive adjective, possessive pronoun:
6.2 Choose the correct word
In sentence 1), Jenny and me/I are the SUBJECT of the verb joined. Therefore, the subject pronoun, I, is correct.
The opposite is true for sentence 2). Justin and me/I are the OBJECTS of took. You will hear many English speakers incorrectly saying “Justin and I.”