Please help. I don't understand how im suppose to apply the doubled amount. And if its 10 years ago, would the amount be -20? I belive the equation is A(t)=Ae^rt but im not sure

Now, martin can reasonably guess that the standard deviation for the entire population of people at the mall during the time of the survey is $1.50. what is the 95% confidence interval about the sample mean? interpret what this means in the context of the situation where 95 people were surveyed and the sample mean is $8. use the information in this resource to construct the confidence interval.