Nearlyse tried to subtract two polynomials. Her work is shown below:
$\begin{align}
&\phantom{=}(3a^2+7a-4)-(-2a^2+4a+9)
\\\\
&=3a^2+7a-4+2a^2-4a-9&\text{Step }1
\\\\
&=(3+2)a^2+(7-4)a+(-4-9)&\text{Step }2
\\\\
&=5a^2+3a-13&\text{Step }3
\end{align}$
**At which step did Nearlyse make an error, if at all?**
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