What is the x coordinate of the solution for the system of equations ?

y-x=9
10+2x= -2y

x=?

Of four points are collinear, they are also coplanar

What is the base of 1/9 to the power of 2

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.