The correct statement that best describes Simone's error is:
Simone did not use the greatest common factor in the equation.
The greatest common factor (GCF) of 24 and 56 is actually 8, which she correctly identified and used in factoring the expression. However, when she wrote the equation as \(24 + 56 = 8(4 + 7)\), she separated 24 into \(8 \times 3\) (which is correct) and 56 into \(8 \times 7\) (also correct), but did not actually calculate the left-hand side correctly.
If she had used the GCF properly, she would have factored both 24 and 56 accurately into terms that would lead to the correct equivalent expression. The left side should be clearly shown as \(8(3 + 7)\). So while she initially used the GCF correctly, the way she presented the factoring was misleading regarding her application of the distributive property. Therefore, the answer still points towards her not applying the greatest common factor correctly in the equation.