A retailer that sells audio and video equipment accumulated 10,451 sales invoices during the previous year. The total of the sales amounts listed on these invoices (i.e., total sales claimed by the company) is $6,384,675. To estimate the true total sales for last year, an independent auditor randomly selects 35 of the invoices and determines the actual sales amounts by contacting the purchasers. The mean and standard deviation of the 35 sampled sales amounts are $532 and $168, respectively.

1. Find a 95% confidence interval for the true mean sales amount per invoice for the 10,451 invoices.
2. Assuming all else remains the same, now find a 99% confidence interval for the true mean sales amount per invoice for the 35 invoices.