I used the U-substitution

Question

x + 1 = u

u^2 -11u + 24

(u + 3)(u - 8)

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

(x + 4) ( X - 7 )

Is this correct?

Answer 1

correct.

Answer 2

There is an apparent mistake in your u-factoring.
u^2 -11u + 24
= (u - 3)(u - 8)
= (x-2)(x-7)