*6. Suppose that the altitude z (in miles above sea level) of a certain hill is described by 2: = f(a:, y) = (0.1)(3:2 my + 2y2). a. Write an equation of the tangent plane at the point P(2, 1, 0.4). Simplify the equation. b. Use differentials to approximate the altitude of the hill above the point (2.2, 0.9) in the my plane