To write this statement in mathematical form let x be the number we don't know. Since we have twice the number this means 2x, then we have to substract 6, that is, 2x-6. This is equatl to 5, then the equation is
[tex]2x-6=5[/tex]Solving for x we have
[tex]\begin{gathered} 2x-6=5 \\ 2x=5+6 \\ 2x=11 \\ x=\frac{11}{2} \\ x=5.5 \end{gathered}[/tex]Therefore x=5.5.
