Since you're told c is the independent varialbe, you need to solve your equation for p:
6c = 2p - 10
6c + 10 = 2p
3c + 5 = p
Now you need to use function notation. Remember that in function notation, you need to use the variable consistently.
f(p) = something with c doesn't match up.
You need
f(c) = something with c in it
Even without doing the first initial work, the only answer that makes c the independent variable is Answer B. But it's also good that Answer B matches our equation above.
