Astore owner is interested in opening a second shop. she wants to estimate the true average daily revenue of her current shop to decide whether expanding her business is a good idea. the store owner takes a random sample of 60 days over a six-month period and finds that the mean revenue of those days is 3,472.00 dollars with variance 315,900.20 square dollars. calculate a 95% confidence interval to estimate the true average daily revenue.

Every confidence interval has associated z value. As confidence interval increases so do the z value associated with it. 
The confidence interval can be calculated using following formula:

Where is the mean value, z is the associated z value, s is the standard deviation and n is the number of samples.
We know that standard deviation is simply a square root of variance:

The confidence interval of 95% has associated z value of 1.960.
Now we can calculate the confidence interval for our income:

The answer would be 13.5 minutes.