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 | 2,889 |
| 2 | 1,015 |
| 3 | 2,657 |
| 4 | 2,658 |
| 5 | 3,500 |
| 12,719 |
The next month (after spending some money on an ad) they sold 7 times as many as they had sold in the previous 5 months. How many more burgers did they sell after running the ad?