What are four specific examples of challenges faced by the main character in The City of Ember?

Doon, the protagonist of The City of Ember, learns that his world is far different than he had believed it to be and must develop a new approach to living. Within that overall challenge, he must take on some specific tasks as well as learn to fend for himself and partner with Lina.
One specific challenge that Doon faces is to provide a power source. He tries valiantly to repair the generator but has to admit defeat because of missing parts and insufficient knowledge. Another challenge is to escape the mayor's forces after they uncover the theft of the city's resources. Doon and Lina escape, but this precipitates the necessity to live off the land while they are on the run.
Once they learn the truth, they are faced with the challenge of how to help their fellow Ember residents; fortunately, they are literate, so they can accomplish this by writing to them about their true situation.