Here is the data:

1st group - 80 ,68, 72, 85, 90, 62, 61, 92,

85, 87, 91, 81, 79, 83,

2nd group - 85, 82, 48, 75, 53, 73, 65,

78, 49, 69, 72, 81, 53, 59,

68, 52, 71, 61, 59, 42,

3rd group - 42, 32 ,36 ,31 ,65 ,29 ,43,

19, 53, 14, 61, 31, 42, 30,

39, 32.

Calculated mean for the stratified sample: y_strata= 59. 989. The st. dev. for the first group sd(1st) = 10.254, sd(2nd ) = 12.578, and sd(3rd) = 14.643. I need to calculate the sample size so that the standard error of the mean would equal 4 points. I need to use proportional allocation. The confidence level is 95%.

How to do this?