Hey! I would really appreciate some help with this question - thanks!

In 2006 Finnair decided to add winglets to its seven Boeing 757-200s: "The high cost of fuel means that the installation will pay for itself after two years. Fuel burn will be reduced by 4-5%, the carrier estimates, and 200 nautical miles will be added to the range." a. Was this a case where the payback rule worked? b. Was there any need for an NPV calculation? c. Could Finnair have generated additional useful information by calculating the NPV of this investment? investment?