Pls help me with 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.

What is the sum of these mixed numbers 4 2/3+ 3 1/9

Find the unit rate. enter your answer as a mixed number. a fertilizer covers 2/3 square foot in 1/2 hour.