Answer:
gcf is 
Step-by-step explanation:
we are given
and 
Firstly, we will find factors of both expression


now, we will find common factors among them
we can see that
For finding gcf, we always find common factors
so,
common terms are 3,m^2 and n
so, gcf is


We have

so this is indeed a difference of squares. Factorizing would give

making the answer D.
We can further factor the first term here and write

but that's clearly out of the scope of this question.
Answer:
-55
Step-by-step explanation:
2nd term=> -1 + -2 × (2 - 1)
3rd term=> -1 + -2 × (3 - 1)
:
28th term=> -1 + -2 × (28 - 1)
=> -1 - 54 = -55