A grocery store's receipts show that Sunday customer purchases have a skewed distribution with a mean of $33 and a standard deviation of $20. Suppose the store had 307 customers this Sunday.

a) Estimate the probability that the store's revenues were at least $ 10,400.

b) If, on a typical Sunday, the store serves 307 customers, how much does the store take in on the worst 10% of suchdays?