20x3 - 70x2 + 60x = 10x(2x2 - 7x + 6) = 10x(2x - 3)(x - 2).
5x(x - 2)
For a start, you can look for a common factor, and separate it. What remains (the other factor) will only be a polynomial of degree 2; I assume you already learned how to factor that.
2(5x + 7)(x - 5)
(2x - 1)(5x + 8)
10x^2 - x - 2 = (5x + 2)(2x - 1)
8x2-10x-3 = (2x-3)(4x+1) when factored
x2-10x-24 = (x+2)(x-12) when factored