Question: You are running for city dog catcher against the incumbent dog catcher. You are told

the polls have you ahead 55% to 45% with an error of 3%, but you want to make certain. After all, this poll may be biased in some way (your mother conducted the poll). You decide to conduct your own poll. How many people must you poll to be 95% confident that the error of your poll is not more than 3%?