A new fast food restaurant opened 5 months ago. The table belows shows the number of burgers they've sold so far.
Month | Burgers Sold |
1 | 3,390 |
2 | 3,977 |
3 | 1,800 |
4 | 2,401 |
5 | 1,318 |
| 12,886 |
The next month (after spending some money on an ad) they sold 3 times as many as they had sold in the previous 5 months. How many more burgers did they sell after running the ad?