The answer is
First let's see the divider of the coeficient:
2 is a prime
32 = 2^5 = 2*2*2*2*2
22 = 11*2
The GCD of all is 2
Now, we have b to the 4, 5 and 6. We can write it:
Now we have all to get the answer:
And the remaining is 2b^4. As you can see, all the monomyals can be divided by 2b^4 and that's the greatest common factor