In Exercises 3–10, use the Chain Rule to calculate the partial derivatives. Express the answer in terms of the independent variables. 3. ∂f ∂s , ∂f ∂r ; f (x, y, z) = xy + z2, x = s2, y = 2rs, z = r2 4. ∂f ∂r , ∂f ∂t ; f (x, y, z) = xy + z2, x = r + s − 2t, y = 3rt, z = s2