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:
| Year (January) | Population (000) | Rural, % | Urban, % | Source |
| --- | --- | --- | --- | --- |
| 1939.0 | 6081.0 | 72.0 | 28.0 | census |
| 1959.0 | 9295.0 | 56.0 | 44.0 | census |
| 1970.0 | 13001.0 | 50.0 | 50.0 | census |
| 1979.0 | 14685.0 | 46.0 | 54.0 | census |
| 1989.0 | 16537.0 | 43.0 | 57.0 | census |
| 1999.0 | 14953.0 | 43.0 | 57.0 | census |
| 2002.0 | 14851.0 | 43.0 | 57.0 | estimate |
| 2005.0 | 15075.0 | 43.0 | 57.0 | estimate |
| 2008.0 | 15572.0 | 47.0 | 53.0 | estimate |
Question:
For how many years was the urban population 57%?
Answer:
4.0