Every Monday, The Energy Information Administration (EIA) determines the national average gasoline price by collecting retain prices for gasoline from a sample of 900 retail gasoline outlets from across the nation. On July 14,2023, the ElA reported the national average retail price for regular-grade gasoline to be 4.043 per gallon. Assume that the population standard deviation is 0.64 per gallon.

Calculate the standard error used to caluclate a $95 \%$ confidence interval abou the average retail price for regurlar grade gasoline.

Step 1 ：The Energy Information Administration (EIA) determines the national average gasoline price every Monday by collecting retail prices for gasoline from a sample of 900 retail gasoline outlets across the nation.

Step 2 ：On July 14,2023, the EIA reported the national average retail price for regular-grade gasoline to be $4.043 per gallon.

Step 3 ：We are assuming that the population standard deviation is $0.64 per gallon.

Step 4 ：We are asked to calculate the standard error used to calculate a $95 \%$ confidence interval about the average retail price for regular grade gasoline.

Step 5 ：The formula for standard error is given by \(\frac{\sigma}{\sqrt{n}}\), where \(\sigma\) is the standard deviation and \(n\) is the sample size.

Step 6 ：Substituting the given values into the formula, we get \(\frac{0.64}{\sqrt{900}}\).

Step 7 ：Solving the above expression, we get the standard error to be approximately $0.0213$ per gallon.

Step 8 ：Final Answer: The standard error used to calculate a $95 \%$ confidence interval about the average retail price for regular grade gasoline is \(\boxed{0.0213}\) per gallon.