500 plates cost $18.00 what does each plate cost

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.

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).

The price of a car has been reduced from $19,000 to $11,590. what is the percentage decrease of the price of the car?