To cover a rectangular region of her yard, penny needs at least 181.5 square feet of sod. The length of the region is 16.5 feet. What are the possible widths of the region? Let the width be x.

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.

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