6 7 6 Consider the function f(x, y,z) = > 4xyz -9, the point P(0, - 4,2), and the unit vector u = 11 11 11 a. Compute the gradient of f and evaluate it at P. b. Find the unit vector in the direction of maximum increase of f at P. c. Find the rate of change of the function in the direction of maximum increase at P. d. Find the directional derivative at P in the direction of the given vector