Question 1206825
For 90% confidence interval, z value is 1.645. You have to know it, look it up.

z*(stddev/squareroot(n)) = the margin of error (MOE)

n is sample size.

Mean +/- MOE is the confidence interval.

15 +/- 1.645*(2/sqrt(10)) = about 13.96 to 16.04