$127.27
Price index is (new year/old year)*100
If 2005 is the base/old year, then:
$700/550 = 1.27273 * 100 = $127.27
Price index is used to show inflation from year to year by the change in price for the same goods in a base year to current year. Price index for the base year compared to the base year will always be 100, so anything above that shows inflation.