The following table shows the number of pens and the number of erasers of 6 different colours that were sold from a stationery store during a given week.
The total number of erasers having colours C3 or C4 is approximately what percentage of the average number of pens of each colour?
| Colours | Pens | Erasers |
| C1 | 20 | 15 |
| C2 | 24 | 21 |
| C3 | 40 | 12 |
| C4 | 22 | 18 |
| C5 | 26 | 27 |
| C6 | 36 | 33 |