1. The problem involves calculating the speed given the time and distance. 2. We know the formula for speed is $$\text{speed} = \frac{\text{distance}}{\text{time}}$$. 3. The distance given is 540 km and the time is 4 1/2 hours, which is $$4.5$$ hours. 4. Substitute the values into the formula: $$\text{speed} = \frac{540}{4.5}$$. 5. Calculate the speed: $$\frac{540}{4.5} = 120$$ km/h. 6. Therefore, the correct answer is B. 120 km/h.