Factorise the following expressions. (i) `7x - 42` (ii) `6p - 12q` (iii) `7a^2 + 14a` (iv) `-16z + 20z^3` (v) `20l^2m + 30a l m` (vi) `5x^2y - 15xy^2` (vii) `10a^2 - 15b^2 + 20c^2` (viii) `-4a2 + 4ab - 4ca` (ix) `x^2yz + xy^2z + xyz^2` (x) `ax^2y + bxy^2 + cxyz`