Please help!! and provide explanation

Describe in detail how you would construct a 95% confidence interval for a set of 30 data points whose mean is 20 and population standard deviation is 3. be sure to show that you know the formula and how to plug into it. also, clearly state the margin of error.

What are the relative frequencies, to the nearest hundredth, of the rows of the two-way table? group 1: a 15 b 45 group 2: a 20 b 25

What is the y intercept of f(x)=(1/2)^x?