is actually -1, because that's the slope of the tangent to f. (It's a straight line, y=mx+c where m = -1 is the gradient, and c = 3 is where that line meets the line x=0, the y axis).

To find , note that as y=-x+3 touches the graph of f at the point where x=2, all you need to do is feed x=2 into the equation for the tangent at that point (which is given), and see what value of y you get out of the end. This is because at x=2, the graph of f(x) and its tangent are at the same point.