After 10 students dropped from the Chinese class, we have: (C - 10) + S + (N + 10) = Total number of students.
That is not true. Just because people dropped from the Chinese class (hence the -10) doesn't mean that they weren't in the Spanish class, so you can't do N+10.
Thank you so much for trying, though. I really appriceate your effort!
BTW, I'm totalkoolnezz, just not signed in.