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 | Broadcast date | Run time | Viewers (in millions) | Archive |
| --- | --- | --- | --- | --- |
| " Episode 1 " | 14September1968 | 21:27 | 6.6 | 16mm t/r |
| " Episode 2 " | 21September1968 | 21:39 | 6.5 | 16mm t/r |
| " Episode 3 " | 28September1968 | 19:29 | 7.2 | 16mm t/r |
| " Episode 4 " | 5October1968 | 19:14 | 7.3 | 16mm t/r |
| " Episode 5 " | 12October1968 | 18:00 | 6.7 | 16/35mm t/r |
Question:
What was the archive for episode with 6.6 million viewers?
Answer:
16mm t/r