5) c (5+3c) + 2 (c²+6)=
$$c \cdot 5 + c \cdot 3c + 2 \cdot c^2 + 2 \cdot 6 = 5c + 3c^2 + 2c^2 + 12 = 5c + 5c^2 + 12$$
Ответ: $$5c + 5c^2 + 12$$