what does 3c+7c+5c=

Thanks, reinout......I think we "c" it now.......(LOL!!)......points and thumbs!!!

remember that

3c = c + c + c

7c = c + c + c + c + c + c + c

5c = c + c + c + c + c

So we can say

3c+7c+5c = c + c + c + c + c + c + c + c + c + c + c + c + c + c + c = (3+7+5)c = 15c

short form of reinouts answer:

3c+7c+5c=15c     ANSWER

btw good one CPhill !

Yes Chris, there should always be time for siliness.  I've given you a couple of thumbs up for you 'fun' efforts.