9 A random sample of five pairs of values of \(x\) and \(y\) is taken from a bivariate distribution. The values are shown in the following table, where \(p\) and \(q\) are constants.
| \(x\) | 1 | 2 | 3 | 4 | 5 |
| \(y\) | 4 | \(p\) | \(q\) | 2 | 1 |
The equation of the regression line of \(y\) on \(x\) is \(y = - 0.5 x + 3.5\).
- Find the values of \(p\) and \(q\).
- Find the value of the product moment correlation coefficient.