why do the people of ember how anger toward the mayer in the town meeting

Are you referring to chapter 6? The mayor's voice kept coming in blasts of incomprehensible sound, and the people in the crowd were either shouting angrily or yelping in fear of being squashed. Someone stepped on Lina's foot, and her scarf was half yanked off. For a few seconds she was afraid she was going to be trampled.

After the lights had gone out for more than twice as long as at any time in the past, the people of Ember were in a somber mood because the electricity being on is the absolute key to their continued survival and they know it. When the Mayor called the town meeting they were expecting to get some real answers as to what was being done to prevent it from happening again. They were irritated that it was not easy to hear the Mayor's voice but some people could understand what the Mayor was saying. He told them not to panic and that "solutions are being found" but he didn't tell them what those solutions were. This is why the people were showing anger. First one woman called out "What solutions?"and then more and more people echoed her question until it became "a chorus, louder and louder". The Mayor was hustled back into Gathering Hall and the crowd roared and began throwing things.