6 (10 points) Company A supplies 40% of the computers sold and is late 5% of the time. Company B supplies 30% of the computers sold and is late 3% of the time. Company C supplies another 30% and is late 2.5% of the time. A computer arrives late - what is the probability that it came from Company A?

7 (10 points) A pilot study conducted a few months earlier indicated that the standard deviation of monthly salary for new college graduates was 1,325 yuan. The research group wants the study's findings to be within 200 yuan of the true mean with a confidence level of 95%. What sample size is required?