The difference between the sample means of two populations is 34.6, and the standard deviation of the difference between sample means is 11.9. What is the 95% confidence interval

Well as i know these intervals show how much of our data are in them

x is mean and b is standard deviation of the distribution

(x-b, x+b) contains about 68 percent of data

(x-2b, x+2b) contains about 96 percent of data

(x-3b, x+3b) contains about 99 percent of data