[latex]3(x+2)=12\\ 3x+6=12\\ 3x=12-6\\ 3x=6\ /:3\\ x=2[/latex]

You multiply 3 by the numbers in the bracket which is 3 × x + 3 ×2 = 12 3x+6 = 12 Collect like terms move 6 to 12 which makes it 12-6 3x= 6 divide both side by three 3x/3 6/3 X = 2