I used different approach to calculate the time of every frame in the mp3 file..
assuming that all frames have same size in the file.. so I just get the total time of the mp3 file in milliseconds.. then calculate total frames in the file and finally divide the total time by total frames.. so the formula would look like:
float frameTime = totalTimeMillisec / totalFrames;
you will get the total time of every frame in the track in milliseconds..
after I done that I got around 52 milliseconds... and that was similar to what Mark Heath said..
anyway thanks everybody for the solutions..