2/5c+4/5c-6=c+7 6/5c=c-13 5/5c=-13 C=-13

Did you sub c = -13 back in to see if it works ??

I bet it won't, since I see a blatant error in your 2nd last line

Hint: don't you think that little c should be changed to 5c/5 ?
Don't you need a common denominator to subtract ?

C=65

correct

Thanks