3. Let f = f(x, y) be a smooth function of two variables x and y, and let x = x(t) and y = y(t) be smooth functions of t. Suppose that x(2) = 1 and y(2) = =1; ic (2) = 2 and y(2) = 3 (where the dot denotes the derivative with respect to t); and (-1, 1) = 3 and ( -1, 1 ) = 4. Find the rate of change of f at t = 2