안녕하세요. E&M강의 7강 2008 frq 해설하실때 기출문제 스코어 가이드라인 보면서 채점을 했는데 note에 적혀있는 내용이 이해가 잘 안되서 질문글 올립니다. 식에는 10r 이라 적었는데 10c는 무엇인가요?

감사합니다. 

Note: The intent of the problem was to ask for the speed at a distance of 10c instead of the stated 10r. Very few students did anything other than treat 10r as if it were outside the shell.

Note: If a student noted that 10 did not define a definite radius, points were awarded as appropriate for attempting a calculation in any region or several regions, or for a clear indication that the solution is region-dependent.