Ok. Some basic rules. The derivative of a constant is zero. That could be 1,2,3, pi, e, phi, etc. - the derivatives of all of these are zero.
If you have a polynomial in the form of , then So you can apply both of these rules to your f(x),g(x), and r(x).
On k(x), is that supposed to be , or ? I can't tell. And on the second f(x) term, is that supposed to be ?