You can put this solution on YOUR website! NOTE: Question edited. if this is not the correct question, please re-post.
X=your age now
X+12yrs=3(X-4yrs)
X+12yrs=3X-12yrs Add 12 yrs to each side.
X+24yrs=3X Subtract X from each side.
24 yrs=2X Divide each side by 2.
12yrs=X ANSWER You are currently 12 years old.