Statistics hard questions?

According to the federal reserve board the avg credit card debt per household in 2010 was 8496; the distribution of debt is know to have a normal distribution and a standard deviation of 2800. a) what is the probability that a randcomly selected household with have more than 13000 in credit card debt? b) the federal reserve wants some kind to system that will alert concumers that have the highest amount of debt and has proposed a system that will send a letter to concumers that are in the top 10% for credit card debt. What amount of credit card should trigger a letter? c) the federal reserve wants to take a random sample of 100 households and calculate the mean credit card debt. What is the probability the that this sample mean will be less than 8000? d) if they were to take a larger sample would the probability in part c) increase, decrease or remind unchanged-----why?