Plz help me?! (who wants to be friends?)

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.

Taylor wants to paint his rectangular deck that is 41 feet long and 24 feet wide. a gallon of paint covers about 350 square feet. how many gallons of paint will taylor need to cover the entire deck? round your answers to two decimal places when necessary.

Prove sin2a + cos2a - 1 / sin2a + cos2a + 1 = 1 - tana / 1 + cota