and 



That's because 

a.  3 is the smaller power of the common prime factor 2.
b.  4 is the smaller power of the common prime factor 7.



That's because

a.  5 is the larger power of the common prime factor 2.
b.  8 is the larger power of the common prime factor 7.
c.  all the other factors of both numbers are included.

3.)  is a factor of 

because a smaller power of a prime is always a factor of a
larger power of the same prime.

Edwin