There are four regions of a certain country that meet at a common corner. The areas of the four regions, in square miles, are shown in the table. Region 1 71,723 (a) Mentally estimate the combined area of the four regions, writing down a sequence of numerals to indicate your thought process. Round to the nearest ten thousand to perform this estimation. Region 2 100,265 Region 3 114,756 Region 4 123,765 (b) Compute the actual sum of the areas in part (a).