I need help on 2 & 3

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.

How to choose the sign of the radical in the denominator of the formula for the distance from a point to a line.

If 25% of y is 30, what is 60% of y?