. It is believed that the average US households' spending on food is 40 dollars per day. Suppose you recently take a random i.i.d. sample of 81 households in the US and the result revealed a mean of 38 dollars per day with the standard deviation of 3 dollars. a. (15/100) Can it be concluded that the average dollars spent per day by U.S. households has changed? (please provide 2 approached both the "T-test (Zscore)" and "P-value" approach. (You should write down the null, alternative, formulas, and provide your p-value on the z graph.) b. (10/100) Create the 95 % Confidence Interval for the population mean using the information above? (Do not forget the complete formula of the interval)