given your answer for part B, doing part C is impossible because there is nothing to factor out.
The place you made the mistake in Part B is when you added 10 and 2m together. You cannot do this,
The answer to Part B would just be "10 + 2m"
now to find the GCF of 10 and 2
2 is divisible by only 2 and 1
10 is divisible by 10,5,2, and 1
the greatest common factor would be 2