What is the resistance of a circuit for which the applied voltage is 12 volts and the current flow is 1.5 amperes?
Why Ohm's Law rearranged for resistance is R = E / I, so divide the voltage by the current: 12 volts / 1.5 amperes = 8 ohms. Whenever the question gives volts and amps and asks for ohms, division is the operation, and the answer must be smaller than the voltage number whenever the current is greater than 1 amp.
Watch out The choice of 18 ohms comes from multiplying 12 by 1.5, which is the power formula P = E x I and gives watts, not ohms; 0.125 is the division done upside down (1.5 / 12).
E over I gives R. Cover R in the E/(I x R) triangle and what's left is E divided by I.