Question 34085
To factor this problem, 100v^2-64y^2 you can see you have the difference of two perfect squares.  When you factor then because there is no middle term you'll have a square root of the first plus the square root of the second times the square root of the first minus the square root of the second.  Another thing to do on a multiple choice test is to multiply the two factors out- you can then rule out the wrong answers and check the right answer.

100v^2-64y^2
(10v + 8y)(10v - 8y)
(A) is correct. 

12a^3 - 4a^2 - 408a
First, I would factor the greatest common factor- the thing that all three have in common. IN this case, 4a. 
4a (3a^2 - a - 102)
Now factor the second part:
4a (3a - 17)(a + 6)

Always double check by multiplying out your factors.