The GCF is 6.
30 over 108 is a fraction. A fraction does not (cannot) have a GCF.
The GCF is 10.
GCF(30, 50) = 10.
The GCF is 10. The LCM is 30.
The GCF is 10.
The GCF is 10.
The GCF of 50 and 30 is 10. (I believe you meant to ask "What ?" instead of "Why ?".)
gcf(20, 30, 90) = 10
The GCF would be 10 !
The GCF is 10.
The GCF is 12.