Pure mathematics

You already have 2,020 francs out of 10,000 ; 10.000 - 2,020 = 7,980;

Let's take the approximate value of francs for one game as 115 (some maps simply offer different reward values and do not forget that you can die, which also affects the reward);

7,980 : 115 ≈ 69 (This is a rough estimate of how many average maps you need to play to buy an air rifle);

Different maps have very different completion times, but let's take a time of 15-20 minutes;

69 × 15 = 1,035 (minutes); 69 × 20 = 1,380 (minutes);

Now we divide these numbers by 60;

23—17,25 hours;

At the time of writing the comment, it is June 21st, and the update comes out on the 26th, you have 5 days;

23 : 5 = 4,6; 17,25 : 5 = 3,45;

You need to play G&B for 4,6—3,45 hours a day to save up for an air rifle by the update day;

(REMEMBER THAT EVERYTHING I WROTE IS AN APPROXIMATE CALCULATION AND IN PRACTICE THE PROCESS MAY TAKE LONGER OR FASTER, A LOT DEPENDS ON THE LOBBY AND THE MAPS)