Carry out the following divisions. (i) `28x^4 -: 56x` (ii) `-36y^3 -: 9y^2` (iii) `66pq^2r^3 -: 11qr^2` (iv) `34x^3y^3z^3 -: 51xy^2z^3` (v) `12a^8b^8 -: (-6a^6b^4)`