What is the problem and solution?

Amidst the intense summer heat, residents of Philadelphia begin to sicken and die from a strange disease that is eventually identified as yellow fever. The fever eventually runs its course after killing thousands of people. Mattie is very happy to reunite with her mother; however, her mother's health will never fully recover, so Mattie now has to take on a much more adult role in managing and running the business. The novel ends with Mattie healthy and hopeful about her future.