3 Robert has a part-time job delivering newspapers. On a number of days he noted the time, correct to the nearest minute, that it took him to do his job. Robert used his results to draw up the following table; two of the values in the table are denoted by \(a\) and \(b\).
| Time \(( t\) minutes \()\) | \(60 - 62\) | \(63 - 64\) | \(65 - 67\) | \(68 - 71\) |
| Frequency (number of days) | 3 | 9 | 6 | \(b\) |
| Frequency density | 1 | \(a\) | 2 | 1.5 |
- Find the values of \(a\) and \(b\).
- On graph paper, draw a histogram to represent Robert's times.