In a sample of 209 gas-powered cars, the monthly average cost of gasoline was $107.33 with a standard deviation of $16.18. In a sample of 52 electric cars, the monthly average cost of electricity was $40.83, with a standard deviation of $9.61. You want to calculate a 90% confidence interval for the average monthly savings from switching from a gas-powered car to an electric car.

1. What is the value of your estimate for the average monthly savings from switching from a gas-powered car to an electric car?

2. What is the value of the standard error of the estimator?

3. What is the t-critical value you would use for the confidence interval?

4. What is the lower bound of the 90% confidence interval?