For a class of 50 students, the cumulative frequency distribution of their science scores is:
| Score | Cumulative frequency |
| 0–10 | 6 |
| 10–20 | 15 |
| 20–30 | 27 |
| 30–40 | 39 |
| 40–50 | 50 |
Determine the mean score of the class.
(a) 32.6
(b) 29.6
(c) 27.6
(d) 33.2