Do yourself a favor and specify the exact problem you are having and update the question with an output of your program after it fails.
Try this:
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (data != null && data.getExtras().containsKey("Days")) {
int i = data.getExtras().getIntExtra("Days", days);
TextView tvD = (TextView) findViewById(R.id.MA_TvDays);
if (tvD != null) tvD.setText("" + i);
}
}