Answer: 3/11
Step-by-step explanation: We can write a ratio using the word to, using a colon, or using a fraction bar. Here, since we want our ratio in simplest form, I would use a fraction bar.
We know that there are 18 buses and there are 66 cars.
So our ratio is simply 18/66.
Notice however that 18/66 is not in simplest form so we need to divide the numerator and the denominator by the greatest common factor of 18 and 66 which is 6 to get the equivalent fraction 3/11.
So the ratio of buses to cars is 3/11