So I only have 3 homework questions left and I can't seem to figure out how to solve. I've tried solving them, but I keep getting them wrong. Any help?

Question

Factor the polynomials:
a) 3x^2 +19x - 40

b) x^4 - 25x^2

Simplify the expression completely:

(1/(x-h)^3 - 1/x^3)/8h

Answer 1

b. Difference of two squares, then one of those factors can be factored as a difference of two squares again. I can check your work.

a. What is ( x+8)(3x-5)

c. do some combination.

((x^3-(x-h)^3)/(8h(x^3*(x-h)^3)

now factor the numerator as a difference of two cubes. Doing it in my head, I see some reduction.

Answer 2

ooh, nevermind I figured out how to do a) answer is 3(x-5)(x+8)....I forgot to move the 3 over
and b) uses the difference of squares formula so the answer is x^2(x-5)(x+5)

still can't figure out the third one though!