$\frac{x^2 - 10x + 25}{3x + 12} * \frac{x^2 - 16}{2x - 10} = \frac{(x - 5)^2}{3(x + 4)} * \frac{(x - 4)(x + 4)}{2(x - 5)} = \frac{x - 5}{3} * \frac{x - 4}{2} = \frac{(x - 5)(x - 4)}{6}$

$\frac{1 - a^2}{4a + 8b} * \frac{a^2 + 4ab + 4b^2}{3 - 3a} = \frac{(1 - a)(1 + a)}{4(a + 2b)} * \frac{(a + 2b)^2}{3(1 - a)} = \frac{1 + a}{4} * \frac{a + 2b}{3} = \frac{(1 + a)(a + 2b)}{12}$

$\frac{y^2 - 25}{y^2 + 12y + 36} * \frac{3y + 18}{2y + 10} = \frac{(y - 5)(y + 5)}{(y + 6)^2} * \frac{3(y + 6)}{2(y + 5)} = \frac{y - 5}{y + 6} * \frac{3}{2} = \frac{3(y - 5)}{2(y + 6)}$

$\frac{b^3 + 8}{18b^2 + 27b} * \frac{2b + 3}{b^2 - 2b + 4} = \frac{(b + 2)(b^2 - 2b + 4)}{9b(2b + 3)} * \frac{2b + 3}{b^2 - 2b + 4} = \frac{b + 2}{9b} * \frac{1}{1} = \frac{b + 2}{9b}$