environmental chemistry

An investigation of how much methane is produced by digesting sludge that first spent 2,10, or 20 days in an aerated pond, with each sludge analyzed in triplicate, yielded the following values: The standard deviation of the 20-day sample is 15.9; for the 10-day sample 21.0, and for the 2-day sample 24.3. Enter the methane production for the three different sludges with 95% confidence intervals. In the example, triplicates were used - how many tests need to be done if the margin of error is to be a maximum of 10%