I have to do a lab to find the resistivity of a wire of an unknown material, I have the cross-sectional area of the wire, the resistance and length of each point on the graph, and the slope of the graph, but I don’t know how the slope fits into the equation for resistivity (ρ = RA/l).
Hard to say without seeing the graph but assuming you are plotting resistance as a function of the length of the wire (measuring the resistance at 100 cm, 200 cm, 300 cm, etc. The slope of the straight line (it should be a straight line) will be in units of ‘resistance units’ / ‘length units’.
Now you can convert the slope to ohm/m. Multiply that by the area in m^2. That gives you the resistivity in ohm – m. If you know the material, check it against the published data to be sure you have it right or post your work here and we can check it.