Consider the polynomial [\(f(x)=1-12x+3x^2-4x^3+5x^4\) and \(g(x)=3-2x-6x^3+9x^4\). Find c such that the polynomial f(x)+cg(x) has degree 3.
Since we know what f(x) and g(x) is, try combining them and see what x value you will get. Then, it will be easy to see what c has to be.
Hope this helped!