Hello, Jkjones,
First thing to remember is that you don't need outside information to solve these LSAT questions - just the information provided will do! Keep that in mind if you ever get confused by a question you happen to have personal knowledge of. Otherwise it will get pretty confusing pretty quickly!
Anyway, I think you meant Question 446, which was the Assumption question about Japanese cars. And you're right, in the stimulus itself, there is no link between side of the road driven on and side of the car the steering wheel is preferred on. That should be a clue that that link should be found in the answer choice.
B is the correct answer choice, because it provides the link between driving on the left side and not preferring left-side steering wheel cars that is required for the conclusion, that NA auto manufacturers should produce more right-side steering wheel cars.
Assumption questions have a formula just like Justify questions do, fortunately! Since you know Justify questions are like:
If [Premises in stimulus] + [Correct answer choice], then [Conclusion in stimulus].
Assumption questions are similar:
If [Premises in stimulus] + [Conclusion in stimulus], then [Correct answer choice].
This is because an Assumption answer choice is a necessary condition, similar to how a Justify answer choice is a sufficient condition. You can see for yourself how this question fits that formula.
Hope that helps,
Lucas Moreau