If you are looking for the answer in the form y = mx + b the answer is: y = -1x + 2
The number before the x is the slope and the slope is given so you would have -1x. To solve for the y intercept (b) you can either draw the graph or simplify from point slope form (y - y1 = m(x - x1). If you draw it, plot a point at (3,-1) and use the slope (up 1 over 1 to the left) to draw the line until it passes though the y axis. This results in the point (0,2).