Choose the property of addition that justifies the equation. (5 + y) + 7 = 7 + (5 + y)
Choose one)
0 + a = a
(Choose one)
(5 + x) + 6 = 5 + (x + 6)
(Choose one)

Answer this question only if you know the 30 points and

Solve 3x-18=2y and 5x-6y=6 by elimination show work

Afactory makes propeller drive shafts for ships. a quality assurance engineer at the factory needs to estimate the true mean length of the shafts. she randomly selects four drive shafts made at the factory, measures their lengths, and finds their sample mean to be 1000 mm. the lengths are known to follow a normal distribution whose standard deviation is 2 mm. calculate a 95% confidence interval for the true mean length of the shafts. input your answers for the margin of error, lower bound, and upper bound.