Let L be the length of the curve y = f(x), q </= x </= u, where f is positibe and has a continuous derivative. Let Sf be the surface area generated by rotating the curve about the x-axis. If c is a positive constant, define g(x) = f(x) + c and let Sg be the corresponding surface area generated by the curve y = g(x), q </= x </= u. Express Sg in terms of Sf and L.

I can't get it. It's a homework problem!