Okay, before I start, I apologize for the long answer, but this is going to have a lot of steps and I want to explain each the best I can.
c=5b+a/f
First thing's first, get rid of any constants.
If we treat a as the variable and anything else that's not attached to it as a constant, this is a whole lot easier.
The only thing that isn't attached to a is 5b. Since 5b is positive, we have to subtract that to get it away from a. We end up with:
c-5b=a/f
Now, we treat f as if it is a coefficient. To get a by itself we multiply each side by f. Doing this we get
c-5b*f=a
I belive the only other answer that would work is f*c-5b=a but don't take my word for.
Any Questions?