A market research survey conducted by a fastfood restaurant took a random sample of 800 orders delivered in a given month. 320 of these orders were placed by clients above the age of 20. Calculate the 95% confidence interval for the proportion of the company's total orders that went to this age group. Select one: a. 0.355, 0.445 b. 0.366, 0.434 c. 0.399, 0.401 d. 0.372, 0.429