Paulina lives in an one-million person European city.
Every third day every second person in the city gets one polythene bag from their local shop.

If all the people in the city decided to use their own bags instead, roughly how many bags would be saved in a year?

Polyethylene or polythene is the most common plastic.
As of 2017, over 100 million tons of polyethylene resins are produced annually.

The weight of bags 6" x 10" x .002 is 8 pounds (3.6kg) per thousand

1 ton = 1,000 kg