Unsure of what you are asking! P=21+2w is the equation of a straight line with slope 2 and y-intercept (0,21). To graph it, plot the y-intercept (0,21). Starting with your pencil on that dot, move your pencil point 1 unit to the right and 2 units up. Plot a dot there. Now draw a straight line through these two dots.
If this does not address your question, please explain in more detail what you're looking for.
