The answer is (x - 1)(3x + 5)
Let's substitute (x + 2) with a:
3(x + 2)² - 10(x + 2) + 3 = 3a² - 10a + 3 =
= 3a² - 9a - a + 3 =
= 3a * a - 3a *3 - (a - 3) =
= 3a(a - 3) - (a - 3) =
= (a - 3)(3a - 1)
Now, substitute a with x + 2:
(a - 3)(3a - 1) = (x + 2 - 3)(3(x + 2) - 1) =
= (x - 1)(3x + 6 - 1) =
= (x - 1)(3x + 5)