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 | Chesterfield | 4–1 | Barrow | 8 December 1956 |
| 2 | Southampton | 3–2 | Weymouth | 8 December 1956 |
| 3 | Watford | 1–3 | Ipswich Town | 8 December 1956 |
| 4 | Reading | 1–0 | Bedford Town | 8 December 1956 |
| 5 | Gillingham | 1–2 | Newport County | 8 December 1956 |
| 6 | Derby County | 1–3 | New Brighton | 8 December 1956 |
| 7 | Swindon Town | 0–1 | Bournemouth & Boscombe Athletic | 8 December 1956 |
| 8 | Accrington Stanley | 2–1 | Oldham Athletic | 8 December 1956 |
| 9 | Brentford | 1–1 | Crystal Palace | 8 December 1956 |
| Replay | Crystal Palace | 3–2 | Brentford | 12 December 1956 |
| 10 | Rhyl | 3–1 | Bishop Auckland | 8 December 1956 |
| 11 | Millwall | 4–0 | Margate | 8 December 1956 |
| 12 | Hull City | 2–1 | York City | 8 December 1956 |
| 13 | Carlisle United | 2–1 | Darlington | 8 December 1956 |
| 14 | Goole Town | 2–2 | Workington | 8 December 1956 |
| Replay | Workington | 0–1 | Goole Town | 12 December 1956 |
| 15 | Scunthorpe & Lindsey United | 0–0 | Wrexham | 8 December 1956 |
| Replay | Wrexham | 6–2 | Scunthorpe & Lindsey United | 12 December 1956 |
| 16 | Blyth Spartans | 0–1 | Hartlepools United | 8 December 1956 |
| 17 | Torquay United | 1–0 | Plymouth Argyle | 8 December 1956 |
| 18 | Hereford United | 2–3 | Southend United | 8 December 1956 |
| 19 | Tooting & Mitcham United | 0–2 | Queens Park Rangers | 8 December 1956 |
| 20 | Peterborough United | 3–0 | Bradford Park Avenue | 8 December 1956 |
Question:
What was the tie number when bradford park avenue was the away team?
Answer:
20.0