what is the answer?

3. A random sample of 12-ounce milkshakes from 14 fast-food restaurants had the following number of calories. 504 399 580 476 450 700 608 472 642 613 Assume the population standard deviation is 90, 591 473 510 375 a) Why it is necessary to check whether the population is approximately normal before constructing a confidence interval? b) Construct a 95% confidence interval for the mean number of calories for all 12-ounce milkshakes sold at fast-food restaurants. (1)