Q is to the first power, so this is a linear equation in Q.
If Q = 0, P = 2. Plot the point (0,2).
Now, with your pencil point on that point, move it to the right 1 unit. At the same time, move your pencil point 0.0025 unit down. Plot a second point there. Draw a straight line thru these two points.
Not as easy as it sounds, because 0.0025 is a very small slope. I'd suggest you use units of 0.0100 along the y-axis.