Ohms law states that plotting current versus voltage is a straight line crossing the origin. In this problem a figure is shown, in the figure current is plotted vs voltge and we can see two points of the line. IN one of the points the voltage in unknown (x). We need to calculate "x" using ohms law formula: R equals to V over I. First we need to look at the point that both coordinates are known which is "B" in this figure. Voltage and current of this point are plugged in the formula and "R" is calculated. "R" can be used for any other point of the line since the resistance of the conductor is constant. Using ohm law again and putting "x" for voltage when we know the amount of the resistance and current makes the problem solved.
