Consider the surface f (x comma y comma z )equalse superscript 4 x plus 2 y minus z baseline minus 1 equals 0, which may be regarded as a level surface of the function wequalsf (x comma y comma z ). the point p(1 comma 1 comma 6 )is on the surface. a. find the (three-dimensional) gradient of f and evaluate it at p. b. the heads of all the vectors orthogonal to the gradient with their tails at p form a plane. find an equation of that plane.