Solve this

One of the CAT questions...

Five years ago, Beth's age was three times that of Amy. Ten years ago, Beth's age was one half that of Chelsea. If C repre- sents Chelsea's current age, which of the following represents Amy's current age?

1. c/6 + 5
2. 2c
3. (c-10)/3
4. 3c-5
5. 5c/3 - 10