3) $$\frac{5a + 5b}{b} \cdot \frac{6b^2}{a^2 - b^2}$$;

$$\frac{5a + 5b}{b} \cdot \frac{6b^2}{a^2 - b^2} = \frac{5(a + b)}{b} \cdot \frac{6b^2}{(a - b)(a + b)} = \frac{5 \cdot 6b^2(a + b)}{b(a - b)(a + b)} = \frac{30b(a + b)}{(a - b)(a + b)} = \frac{30b}{a - b}$$