All else being equal, a study with which margin of error would give you the most confidence in the results?

If the cost to mail a package is an initial $5 and $0.28 for every pound the total cost to mail a package was $11.27, how much did the package weigh?

Car a and car b were in a race .the driver of car b claimed that his car was twice as fast as car a

If 7x=9y, y/z = 7/5 , then x/z = (a) 2/7 (b) 7/9 (c) 9/5 (d) 9/7 (e) 5/9