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 | 3,637 |
2 | 3,152 |
3 | 3,848 |
4 | 2,805 |
5 | 3,942 |
| 17,384 |
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 fewer burgers did they sell before running the ad than they did after running it?