3. Let f(x, y) = In 2x + 4y, find the directional derivative of f(x, y) in the direction of <-3, 4> at the point (-1, 1).

At the point (1,3), the function f(r, y) increases most rapidly in the direction of (-2, 1) at the rate of change equals to 5. Find the directional derivative of f at (1,3) in the direction of (–3, 4).