Replace f(x) with 0 and solve for x. We do this because the x intercepts always occur when y = 0. Keep in mind that y = f(x).
f(x)=x^3-9x^2+20x
0=x^3-9x^2+20x
x^3-9x^2+20x = 0
x(x^2-9x+20) = 0 .... factor out GCF x
x(x-5)(x-4) = 0 ... factor the stuff inside
x = 0 or x-5 = 0 or x-4 = 0 ... zero product property
x = 0 or x = 5 or x = 4
The roots or zeros are 0, 5, 4
Answer: Choice D
