Factorise. (i) `x^2 + xy + 8x + 8y` (ii) `15xy - 6x + 5y - 2` (iii) `ax + bx - ay - by` (iv) `15pq + 15 + 9q + 25p` (v) `z - 7 + 7xy - xyz`

Explanation

Let's factorize each part step by step.

### (i) Factorise `x^2 + xy + 8x + 8y`

1. **Group the terms**:
\[ (x^2 + xy) + (8x + 8y) \]
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