I'm not sure how to answer your question because you didnt specify if you're looking for the value of a, b, or c.
If you're looking for the value of C:
1. Multiply both sides by C
ca=8c-b
2. Subtract 8C from both sides.
ca-8c=-b
3. Factor out the common term C.
c(a-8)=-b
4. Divide both sides by A-8.
Answer= c=b over a-8