What is the greatest common factor of 56, 14, 35, and 84?

Using Prime Factorisation, find each of the following:
56 = 2 x 2 x 2 x 7 = 2³ x 7
14 = 2 x 7
35 = 5 x 7
84 = 2 x 2 x 3 x 7 = 2² x 3 x 7

Rewriting them again:
56 = 2³ x 7
14 = 2 x 7
35 = 5 x 7
84 = 2² x 3 x 7

Taking the lowest power 
GCF = 2 x 7 = 14

Ans: 14