Three mutually exclusive new designs for an aircraft engine are under consideration. The engine has a ten-year life. The first engine incurs a cost of $1.2 million for a net saving of $300,000 per annum as compared to an existing engine. The second design would cost $1.5 million for a net saving of $400,000 per annum. The third has a cost of $2.1 million for a net savings of $500,000 per annum. Use MARR of 18%. How to find the best alternative based on IRR & NPW methods.