What symbol does 9999 use to calculate 24 points

What symbol does 9999 use to calculate 24 points

1、√9×9-9÷√9
2、√9×﹝9-9÷9﹞
3、9+9+9-√9
4、9×9÷√9-√9
5、√9×9×9-√9
6、9+9+√9+√9