A researcher in Denmark is studying the reading habits of the people in the country. His sample that comprises three different cities—Aarhus, Esbjerg, and Copenhagen. Assume there are 150 households in Aarhus, 40 in Esbjerg, and 85 in Copenhagen. The researcher randomly selected 20 households from Aarhus, 10 from Esbjerg, and 15 from Copenhagen and recorded the weekly average reading times (in hours) for each households. From the record, he found that the weekly average reading time for Aarhus is 35.73 hours, Esbjerg is 26.24 hours, and Copenhagen is 18.31 hours. The sample standard deviations for Aarhus, Esbjerg, and Copenhagen were 1.56 hours, 4.78 hours, and 2.49 hours, respectively. 

a. Estimate the mean reading time spent by the households in the city using an unbiased estimation procedure.
b. Find a 90% confidence interval for the mean reading time spent in the city.
c. Find the 95% confidence interval for the total amount of time spent by the people of each city in reading.