1) $5a^2 - 7a - 9 + 2a^2 - 6a + 1 = $

2) $\frac{a}{5} - \frac{2}{3}b - \frac{3a}{10} - \frac{5b}{6} = $

3) $\frac{3}{5}(10a^2 - 5a + 15) - \frac{3}{4}(4a^2 - 18a - 12) = $

4) $13 - 4x(x - y)y - 4y(x - 2y)x - 7 = $

5) $40a^3 - 5(2a - 3)(4a^2 + 6a + 9) = $

6) $2(7a - 5b - 6c) - 3(2a - 3b + 4c) = $

7) $(a - 3)(a + 3)(a^2 + 9) = $