You multiply the length of the model car by the meters from the actual car. It’s easier to convert one unit of measurement to match with the other. I found it easier to convert 18.2 cm to meters which is 0.182 m. Now we multiply 0.182m by 0.3m to get the length of the actual car.
The answer would be 0.0546m. Or if you prefer centimeters, then the answer would be 5.46 cm. Either way is fine.
Hope this helped, please let me know if I was correct. :D