We are given the steps for the solution of a linear equation. Let's analyze lines 3 to 4:
[tex]-6x+10=4x+20[/tex]To continue solving for "x" we need to add 6x to both sides, like this:
[tex]\begin{gathered} 10=4x+6x+20 \\ 10=10x+20 \end{gathered}[/tex]In line 4 we have:
[tex]10=-2x+20[/tex]This means that instead of adding 6x, Andre subtracted 6x.