Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Tie no | Home team | Score | Away team | Date |
| --- | --- | --- | --- | --- |
| 1 | Derby County | 0–1 | Leeds United | 18 February 1975 |
| 2 | Everton | 1–2 | Fulham | 15 February 1975 |
| 3 | Ipswich Town | 3–2 | Aston Villa | 15 February 1975 |
| 4 | West Ham United | 2–1 | Queens Park Rangers | 15 February 1975 |
| 5 | Mansfield Town | 0–1 | Carlisle United | 15 February 1975 |
| 6 | Arsenal | 0–0 | Leicester City | 15 February 1975 |
| Replay | Leicester City | 1–1 | Arsenal | 19 February 1975 |
| 2nd replay | Leicester City | 0–1 | Arsenal | 24 February 1975 |
| 7 | Peterborough United | 1–1 | Middlesbrough | 15 February 1975 |
| Replay | Middlesbrough | 2–0 | Peterborough United | 18 February 1975 |
| 8 | Birmingham City | 2–1 | Walsall | 15 February 1975 |
Question:
What was the tie number when peterborough united was the away team?
Answer:
Replay