Can someone explain to me how to do this

Scores on the cognitive scale of the bayley-scales of infant and toddler development range from 1 to 19, with a standard deviation of 3. calculate the margin of error in estimating the true mean cognitive scale score, with 99% confidence, if there are 12 infants and toddlers in a sample.

Kerion has a beaded necklace business. she can make 12 necklaces is 2 hours. how long will it take her to make 9 necklaces?

Acompany that makes? hair-care products had 5000 people try a new shampoo. of the 5000 ? people, 35 had a mild allergic reaction. what percent of the people had a mild allergic? reaction?