The clinical literature reports that the duration of a typical cold is roughly 18 days. researchers wanted to know if people tend to underestimate the duration of a typical cold, on average. they surveyed a random sample of 352 healthy adults in georgia and asked them how long they think that a typical cold lasts. the researchers reported a 95% confidence interval of 6.9 to 8.2 days for the mean expected duration of typical cold.

find the numerical value of the margin of error for the confidence interval.