解方程~~[請進]急..幫手!!!

8.
x² + 10x + 21 = 0
(x + 3)(x + 7) = 0
x = -3 or x = -7


10.
x² - 17x + 60 = 0
(x - 5)(x - 12) = 0
x = 5 or x = 12


12.
x² - 7x - 30 = 0
(x + 3)(x - 10) = 0
x = -3 or x = 10


14.
x² - 2x - 15 = 0
(x + 3)(x - 5) = 0
x = -3 or x = 5

Hint: factorize them.