Let x be the age of the car (in months), and

let y be the age of the tires (in months, again).


When the car was as old as the tires are now ?  --- Obviously, (x-y) months ago.



So, according to the first part of the condition

    x = 3*(y - (x-y)).


Simplify it:


    x = 3*(2y-x)  

    x = 6y - 3x

    x + 3x = 6y

    4x = 6y

    2x = 3y.           (1)


When the car's tires will be as old as the car is now ?  ----  In (x-y) months, obviously.


So, according to the second part of the condition,

    x + (x-y) = y + 12    months.


Simplify it:


    2x - y = y + 12,

    2x - 2y = 12.      (2)



From equation (1), substitute 2x = 3y into equation (2), replacing 2x by 3y there.  You will get then


    3y - 2y = 12,

     y      = 12.


Thus, the tires current age is 12 months.


Then from (1),  2x = 3y = 3*12 = 36;  hence,  x = 36/2 = 18.


ANSWER.  The car is 18 months old.  The tires are 12 months old.