Victoria tried to subtract two polynomials. Her work is shown below:
$\begin{align}
&\phantom{=}(7a^2+4ab-b^2)-(2a^2-3ab+6b^2)
\\\\
&=7a^2+4ab-b^2-2a^2-3ab+6b^2&\text{Step }1
\\\\
&=(7-2)a^2+(4-3)ab+(-1+6)b^2&\text{Step }2
\\\\
&=5a^2+ab+5b^2&\text{Step }3
\end{align}$
**At which step did Victoria make an error, if at all?**
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