How much longer until I see my abs?

I am 16 years old. I am 171 and I weigh 64 kgs. I workout 4 times a week, in those workouts i do 75 crunches each workout. I have a bit of belly fat above my abdominals, so I have now started the cross trainer just a couple of days ago. I am thinking of doing it also 4 times a week after my workouts. When doing the cross trainer I do it for 25 minutes and have a pretty high level. Do you think I do the cross trainer enough or should I increase the time or amount I do it in a week? How much longer do you think it will take until I see my abs and the results?