Confidence in Simulation Results

Scenario: A project team developed a detailed construction plan that includes activities with uncertain duration's, including precedence constraints. The plan was simulated 10 times, and using a significance level of 0.05, the expected project duration was found to be:
- 365 ± 47 days
In other words, the true mean duration could be anywhere between 318 days and 412 days. Moreover, this is only the mean duration. Given any particular outcome, actual duration could be quite different. We would like to calculate the expected duration with only 20 total days of error. Please provide the number of simulation replications (n) required to accomplish this.

Hi, I need some assistance with the above question please. I was looking to use the proportion data method and calculate the standard deviation from original half-width. However, I am lost on setting this up in excel.