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:
| Episode no. | Airdate | Viewers | BBC Three weekly ranking | Cable rank |
| --- | --- | --- | --- | --- |
| 1.0 | 24 March 2011 | 783000.0 | 8.0 | 17.0 |
| 2.0 | 31 March 2011 | 898000.0 | 4.0 | 17.0 |
| 3.0 | 7 April 2011 | 854000.0 | 6.0 | 16.0 |
| 4.0 | 14 April 2011 | 1065000.0 | 4.0 | 12.0 |
| 5.0 | 21 April 2011 | 983000.0 | 8.0 | 18.0 |
| 6.0 | 28 April 2011 | 1043000.0 | 7.0 | 17.0 |
| 7.0 | 5 May 2011 | 1120000.0 | 5.0 | 14.0 |
Question:
What is the highest cable ranking?
Answer:
18.0