Distributive property:
[tex]a(b+c)=ab+ac[/tex]Commutative property:
[tex]x+y=y+x[/tex]So, using the previous properties:
[tex]\begin{gathered} 2(x+1)+2x=2\cdot x+2\cdot1+2x \\ \text{add like terms:} \\ (2x+2x)+2 \\ 4x+2\equiv4x+2 \end{gathered}[/tex]