What are common factors of 36 and 14

There's only one common factor for 36 and 14 and it is:

2

justification:
because the prime factorization of 36 is: 2 x 2 x 3 x 3
        and the prime factorization of 14 is: 2 x 7 

the only factor that they have in common is 2
therefore the common factor of 36 and 14 is 2