At the point (1, 2), the function (x, y) has a derivative of 2 in the direction

At the point (1, 2), the function ƒ(x, y) has a derivative of 2 in the direction toward (2, 2) and a derivative of -2 in the direction toward (1, 1).

a. Find ƒ_x(1, 2) and ƒ_y(1, 2).

b. Find the derivative of ƒ at (1, 2) in the direction toward the point (4, 6).