Exercise 13.4.3 Given: f(x, y) = x3y, evaluate f(1, 2), f(1.05, 2.1), and calculate z. Use dz to approx- imate Az. Exercise 13.4.4 Using differentials estimate f (3.01, 2.03, 0.96) if we know that f (3, 2, 1) = 7, fx (3, 2, 1) = 2, fy (3, 2, 1) = -1, and fz(3, 2, 1) = 3