The function $f(x) = \frac{6x^3+4x^2-11x+5}{3x^3-15x+20}$ has a horizontal asymptote $y = c$.  What is $c$?
To find the horizontal asymptote of a rational function, I need to compare the degrees and leading coefficients of the numerator and denominator. The degree of both the numerator and denominator is 3, so the horizontal asymptote is the ratio of their leading coefficients. The leading coefficient of the numerator is 6, and the leading coefficient of the denominator is 3, so $y = c = \frac{6}{3} = 2$. 