39. how much would it cost to put hard wood in the living room if the cost of hard wood is 3.99 per square foot?

40. how much would baseboards cost for the bedroom if 1 foot of baseboard costs $7?

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.