Помогите решить примеры

Решите задачу:

$\frac{2(x^2-9)^2}{3(x+2)} : \frac{y(x^2-9)(x^2+9)}{6x(x+2)} = \frac{2(x^2-9)\cdot 6x(x+2)}{3(x+2)\cdot y\cdot (x^2-9)(x^2+9)} = \frac{4x}{y(x^2+9)} \\\\\\ \frac{a-4}{a^2+4a+16} + \frac{12a}{a^3-64} - \frac{1}{a-4} = \frac{a-4}{a^2+4a+16} + \frac{12a}{(a-4)(a^2+4a+16)} - \frac{1}{a-4} =\\\\= \frac{(a-4)^2+12a-(a^2+4a+16)}{(a-4)(a^2+4a+16)} = \frac{a^2-8a+4+12a-a^2-4a-16)}{(a-4)(a^2+4a+16)} = \\\\=\frac{-12}{(a-4)(a^2+4a+16)}$