In A Tree Grows in Brooklyn, how does Francie change because of the death of Johnny; the working world; and meeting and breaking up with Lee? ...

As far as the working world is concerned, Francie learns about seniority, fairness, and the importance of reputation.  Francie becomes disillusioned with the world of work after she has to cross the Brooklyn Bridge to get to work.  She previously thought that the trip would be exciting, but quickly learns that the commute is draining.  Once at work, Francie is happy that she is getting paid so much because she has never before earned such a high salary.  However, after talking to the other girls, she realizes that she is the lowest paid reader and that she has not been treated fairly.  She becomes especially bitter when she realizes that she is a much faster worker than many of the highest paid workers.  Francie, even though she feels used, has no voice in the company and must continue reading for her low salary.  She often looks at the top reader, who has a relationship with the boss, and wishes that she could have her position.  So the working world introduces Francie to the hardships of the "dog-eat-dog" work mentality.