Let's simplify the expression \( 4x^2 - 3x^2 + 5x - 24 \) first.
1. Combine like terms:
\[
4x^2 - 3x^2 = (4-3)x^2 = 1x^2 = x^2
\]
So, the expression simplifies to:
\[
x^2 + 5x - 24
\]
Next, we will factor \( x^2 + 5x - 24 \).
To factor this quadratic expression, we look for two numbers that multiply to -24 (the constant term) and add to 5 (the coefficient of x). The two numbers that satisfy these conditions are 8 and -3.
Thus, we can write:
\[
x^2 + 5x - 24 = (x + 8)(x - 3)
\]
Now, we can compare it with the options given in the question:
1. \( (x+6)(x-4) \)
2. \( (x+8)(x-3) \)
3. \( 4x(x-6) \)
4. \( 2(x-12) \)
From our factorization, we see that the expression \( x^2 + 5x - 24 \) simplifies to \( (x+8)(x-3) \).
Therefore, the correct answer is:
\[
\boxed{(x+8)(x-3)}
\]