The average zinc concentration recovered from a sample of me

The average zinc concentration recovered from a sample of measurements in 36 different location of a river is found to be 2.6 grams per millimeter. Answer the followings, assuming that the population standard deviation is 0.3 gram per millimeters. Obtain a 99% confidence interval for the mean zinc concentration in the river. How large a sample is required if the width of the confidence interval in Part (i) is to be 0.2?

Solution

Given that n = 36    s = 0.3    x = 2.6

x-bar ± t_0.01 ( s/n)

2.6 ± 2.719(0.3/36)

2.6 ± 2.719(0.05)

2.6 ± 0.1360

[2.4640 , 207360]

i didn\'t get the answer for part ii