The total cost to go horseback riding is z dollars per hour plus a $2 fee for renting a helmet. Which expressions represent the cost, in dollars, for 4 people to go horseback riding for 3 hours each?

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.