в) $$(2-y)(y-8) = 2y - 16 - y^2 + 8y = -y^2 + 10y - 16$$
г) $$(a-4)(2a+1) = 2a^2 + a - 8a - 4 = 2a^2 - 7a - 4$$
Ответ: в) $$-y^2 + 10y - 16$$, г) $$2a^2 - 7a - 4$$