the z value for 95% CI = 1.96 ( need to get this from the Z-table)
the standard deviation is given as 0.2
number of samples is given as 49 bottles
now you multiply the Z value by the standard deviation divided by the square root of the number of samples
1.96 x (0.2/sqrt(49) = 1.96 x (0.2/7) = 1.96 x 0.028571 = 0.057
so the answer would be B 24 +/- 0.057
