Factorise the following expressions: (i) p² + 6p + 8 (ii) q² - 10q + 21 (iii) p² + 6p - 18

(i) p² + 6p + 8 = p² + 2p + 4p + 8 = p(p + 2) + 4(p + 2) = (p + 2)(p + 4)
(ii) q² - 10q + 21 = q² - 3q - 7q + 21 = q(q - 3) - 7(q - 3) = (q - 3)(q - 7)
(iii) p² + 6p - 18 This expression cannot be factored easily using integers. It could be solved using the quadratic formula or completing the square, but the original question's solution contains errors and inconsistencies with the given expressions and cannot be reliably reproduced.