Is the overall cost of living higher or lower for urban areas in particular geographical regions of the United States? 

a. Begin to answer this question by first selecting 40 urban areas from the given frame provided in the file P8-28.XLS (Source: ACCRA Cost of Living Index). The urban areas you select should be stratified by geographical location within the United States (e.g., northeast, southeast, mid-west, northwest, or southwest) and should reflect proportional sample sizes. Note that you will need to assign the given urban areas to one of any number of such geographical regions before you can generate a stratified sample. 

b. Explain how one could apply cluster sampling in selecting a sample of size 40 from this frame. What are the advantages and disadvantages of employing cluster sampling in this case?