In 2018, an average of $ 11,250 (per quarter) was spent nationally on food. According to the National Survey of Household Income and Expenditure carried out in 2018, the average quarterly expenditure on food for the 2,857 selected households in the state of Mexico was $ 13,485 and the standard deviation was $ 12,000. 

a) Establishes the hypotheses to test whether food spending in the state of Mexico is higher than spending at the national level. 

b) Calculate the test statistic. 

c) At a significance level of 10%, what is the conclusion? (Don't forget to interpret the results). 

d) Calculate a 90% confidence interval for the average quarterly expenditure on food in the state of Mexico.