Resposta:  3

Explicação passo a passo:

2x+1=7

2x=7-1

2x=6

x=6/2

x=3

[tex]\Large\displaystyle\text{$\begin{gathered} \sf{ 2x+1=7} \end{gathered}$}[/tex]

[tex]\Large\displaystyle\text{$\begin{gathered} \sf{2x=7-1 } \end{gathered}$}[/tex]

[tex]\Large\displaystyle\text{$\begin{gathered} \sf{ 2x=6} \end{gathered}$}[/tex]

[tex]\Large\displaystyle\text{$\begin{gathered} \sf{x=\frac{6}{2} } \end{gathered}$}[/tex]

[tex]\Large\displaystyle\text{$\begin{gathered} \sf{ x=3} \end{gathered}$}[/tex]