Respuesta :

The answer is 3.
3×3=9
3×9=27
3×21=63
AL2006
The factors of 9 are 1,  3,  and 9 .

The factors of 27 are 1,  3,  9,  and 27 .

The factors of 63 are 1,  3,  7,  9,  21,  and 63 .

The common factors of 9, 27, and 63 are 1,  3,  and 9.

Their greatest common factor is  9  .