Geometric sequence of 1.2,2.4,4.8,9.6

Evaluate the expression for the given value of the variable 2×(c2-5) for c=4

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.

The measurement of one angle of a right triangle is 42° what is the measurement of the third angle? (there is no picture)