How long will I have braces for?

So my dentist suggest I get two of my back teeth out my, 6 on my left and seven on my right. My teeth have always had problems and the teeth she wants to take out won't last me for much longer (until I'm about mid twenties so like ten years). If I get those teeth out I have to get braces to pull my teeth back, my mouth is very cramped at the front. I was wondering how long I would have to wear braces for as my dentist said two-three years but wasn't sure.

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