how i minus the time when hit an object?

When a player got the wrong answer(object) time will minus about 5 seconds, how can i do this?

You would have

var Timing:float = 50; //for 50 sec obvisously

function Update(){
   Timing-= Time.deltaTime;  // Every frame remove the delta time
   if(wrongAnswer)           // if wrong answer remove 5 sec
      Timing-=5;
   if(Timing<=0)             // Time out
      Debug.Log("You are a loser");
}