I used the U-substitution

x + 1 = u

u^2 -11u + 24

(u + 3)(u - 8)

( x + 1 + 3) ( x + 1 - 8)

(x + 4) ( X - 7 )

Is this correct?

correct.

There is an apparent mistake in your u-factoring.

u^2 -11u + 24
= (u - 3)(u - 8)
= (x-2)(x-7)

To check if your answer is correct, we need to go through the steps of u-substitution. Here's how you can do that:

1. Start with the equation:
u^2 - 11u + 24

2. Substitute x + 1 = u. This will give you:
(x + 1)^2 - 11(x + 1) + 24

Expanding this equation, you will get:
(x^2 + 2x + 1) - 11x - 11 + 24

Simplifying further:
x^2 + 2x + 1 - 11x - 11 + 24

Combining like terms:
x^2 - 9x + 14

3. Now you need to factorize this quadratic equation:
The factors of 14 that add up to -9 are -2 and -7. So the factored equation becomes:
(x - 2)(x - 7)

Therefore, the correct factored form is (x - 2)(x - 7), not (x + 4)(x - 7) as you wrote.