The following question applies to a normal distribution of statistics test scores with a mean of 100 and a standard deviation of 40.

The teacher decided to give the top 30% of the class a grade of A, the next 40% of students a grade of B, and the final 30% a grade of C. What are the test scores that correspond to these grade cut-offs?

Example questions I found on google always specified how many students actually took the test. But since it does not specify that in this question, how would I go about solving this?

Any help would be greatly appreciated.