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 | 3,632 |
2 | 3,627 |
3 | 3,126 |
4 | 3,151 |
5 | 3,935 |
| 17,471 |
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 fewer burgers did they sell before running the ad than they did after running it?