The best statement that describes Simone's error is:
Simone did not use the correct factors for 60 in the equation.
Simone factored out 4 correctly from 28 (which is \(4 \times 7\)), but the expression she formed for 60 is incorrect because \(60 = 4 \times 15\), not \(4 \times 20\). Therefore, the addition should be \(7 + 15\) for \(28 + 60\) after factoring out the 4 correctly.