A country's exports and imports of energy (combined totals of fossil fuels, hydro, and nuclear, all measured in petajoules) over a five-year period are shown. a. Using 2012 as the base year, construct index numbers for each of the exports and imports. (Enter your responses rounded to one decimal place.) 2012 11,239 Imports Exports Exports Index Number Imports Index Number 3,720 2013 11,723 3,560 2014 11,826 3,277 2015 12,232 3,443 2016 12,531 3,668