As a green-minded driver, Gerry has a dilemma.

He wants to buy a new eco model with emissions of 80 CO₂ g/km instead of his current car that produces 120 g/km.

An article in the Telegraph says that production of a new car generates about 720kg for every £1,000 you spend on it.
The new car costs £20,000 and he usually drives 10,000 km every year.

How many years does he need to drive to make the purchase ecologically reasonable?