It seems that you have missed the necessary details for us to answer this question, but hope this would help you. The line in the given passage that is considered a flashback is this: <span> She thought of her last day in middle school, seven years ago, when Sarah had given her an iPod. Have a great day!</span>
Two symbols that are important in The Great Gatsby are the color green and a clock. Green is important as it represents money and Gatsby's hope. These two ideas are tied together because Gatsby believes that if he builds himself into a rich enough person, Daisy will take notice and come back to him. Green is also the color of the light at the end of Daisy's dock which acts as a symbol for her and the love Gatsby is holding out for her. At the end of the novel it says "Gatsby believed in the green light, the orgastic future that year by year recedes before us." This quote shows that the light represents hope, but that that hope keeps getting further and further away instead of getting closer. In the same way money can be lost, so can the promise of the future you want. Green ties these ideas together to symbolize Gatsby's hope.
The clock on Nick's mantle also serves as an important symbol for time. Gatsby is trying to make up time when he meets Daisy again, and a reoccurring theme in the novel is that you can't repeat the past. When Gatsby and Daisy meet again for the first time in many years, Gatsby knocks Nick's clock off its mantle. This represents the time that he and Daisy have lost, and how it is going to slip away from them again. Later, Gatsby says "‘Can’t repeat the past?’ he cried incredulously. ‘Why of course you can!’" in response to Nick's telling him that it would be impossible to do just that. This falling clock shows how desperate Gatsby is to make up that time and how precarious trying to do that is.
