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:
| Frequency (Hz) | R (Ω/km) | L (mH/km) | G (μS/km) | C (nF/km) |
| --- | --- | --- | --- | --- |
| 1 | 172.24 | 0.6129 | 0.000 | 51.57 |
| 1k | 172.28 | 0.6125 | 0.072 | 51.57 |
| 10k | 172.70 | 0.6099 | 0.531 | 51.57 |
| 100k | 191.63 | 0.5807 | 3.327 | 51.57 |
| 1M | 463.59 | 0.5062 | 29.111 | 51.57 |
| 2M | 643.14 | 0.4862 | 53.205 | 51.57 |
Question:
What is the c (nf/km) when the r (ω/km) is 463.59?
Answer:
51.57