Find an equation of the horizontal asymptote

Hey guys, forgot how to do this. All I remember is that the problem is given in factor form and product form and you have to choose the easier one to work with, but I'm totally drawing a blank on what to do. I know that a horizontal asymptote will be of the form y = x, but thats about it. Any help much appreciated.

Let R(x) = (4x^2)(2x - 1)/7(5x + 3)(x + 2)^2 = (8x^3 - 4x^2)/(35x^2 - 119X^2 + 56x + 84)

Find an equation of the horizontal asymptote of R(x).