Find the rate of change of the function f (x, y, z ) = x^2 + y^2 + z^2 at the

point (3,5,4) along the curve of intersection of the surfaces 2x^2 - y^2 + 2z^2 = 25 and x^2 - y^2 + z^2 = 0.

I don't know where to start with this one. If someone can lead me in the right direction that would be great. Thanks.