8. 10a + 15c = 5(2a + 3c)
9. 4a² - 9b² = (2a - 3b)(2a + 3b)
10. 4a² + 28ab + 49b² = (2a + 7b)²
11. b(a + c) + 2a + 2c = b(a + c) + 2(a + c) = (a + c)(b + 2)
12. 5a³c - 20acb - 10ac = 5ac(a² - 4a - 2)
13. x² - 3x - 5x + 15 = x(x - 3) - 5(x - 3) = (x - 3)(x - 5)
14. 9a² - 6ac + c² = (3a - c)²