F(x) = x°-9x g(x) = x2 - 2x-3
Which of the following expressions is equivalent to f(x)/g(x), for x > 3

F(x)=x^3-9x
and
g(x)=x^2-2x-3

so you just need to divide f(x) by g(x)

Therefore:

f(x)/g(x) = (x^3-9x) / (x^2-2x-3)

and of course you need to factor these two function to see if some factor would cancel another

x^3-9x = x(x^2-9)=x(x-3)(x+3)
and
x^2-2x-3 = (x-3)(x+1)