David sold a $1.50 comic book to ronald. having no change for ronalds $5 dollar bill, david got the change at the store. he gave ronald the comic and $3.50. then the store owner told david that the $5 dollir bill was counterfeit. so david gave him five $1 bills. how much money did david make or lose is these transactions?

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.