Brianna built a garden in their backyard that measured 400 cm by 400 cm and built a fence around it.
Later on, they decided to change the size of it to 4 meters by 6 meters.
How much extra fence do they need to buy to build around their new garden?
two of the sides are enlarged from 4 m to 6 m
2 (6 m - 4 m) = ?