Which ordered pair is the solution to the system of equations?

{x+y=−1
{3x−y=21

a. (5.5, −6.5)

b. (7, −8)

c. (10, −11)

d. (5, −6)

Select the margin of error that corresponds to the sample mean that corresponds to each population: a population mean of 25, a standard deviation of 2.5, and margin of error of 5%