Conceptual Physics (12th Edition)

6 ohms, also written as $6 \Omega$.
$$Current = \frac{voltage}{resistance}$$ Rearranging to solve for the resistance, we obtain $$Resistance= \frac{voltage}{current}$$ Put the numbers in from this problem. $$Resistance= \frac{120 V}{20 A} = 6 \Omega$$