This is significant because the absence of everyone else marks how few friends Gatsby really had. For all the people he knew and entertained, only Nick and a man who admired Gatsby's library were in attendance. This is also significant because it illustrates how few true friends we are actually blessed with during our lifetimes
Assuming that you are asking for help identifying the keys, the items are asking for you to draw either a flat or sharp sign in front of the note (depending on the question) and to identify what letter note it represents. The letter notes of the treble clef (starting from line 1, the bottom line) are E, F, G, A, B, C, D, E, and F. The line acronym is Every Good Boy Does Fine, and the space acronym is FACE. The letter notes of the bass clef (starting from line 1, the bottom line) are G, A, B, C, D, E, F, G, and A. The line acronym is Good Boys Do Fine Always, and the space acronym is All Cows Eat Grass. For example, on the second note of question three, you would draw a flat sign in front of the note, and write its letter note, A, on the line below it. If you would like the answers directly, please don't hesitate to ask.