A car buyer is considering whether or not to spend extra for a hybrid in order to save money in the long run on gasoline expenditures. The buyer drives 25,000 km/year. The cost difference between the two vehicles is $4000, and the fuel consumption is 7.9 L/100 km for the ICEV and 5.3 L/100 km for the HEV. The cost of fuel is $0.80/L (about $3/gal). What is the simple payback for buying the HEV, in years