the answer would be x=6 :)
You’d need to add 6 to both sides of the equation, then simplify, then divide, and finally simplify again.
here’s how it would look!
3x=12+6 (add 6 to both sides)
3x=18 (simplifying)
x= 18/3 (dividing both sides by 3)
x=6 (simplifying again to get x)