I think everyone who is coming up with 36 is putting too much conjecture into the equation. The only answer that makes sense is 18, as many of us have said. We've performed the function as presented in the equation, then adding up the individual numbers in the answer. Admittedly, that's a conjecture as well, but since we have the answers for the first two functions given, our method is the only way to come up with an answer with a minimal amount of conjecture or extrapolation the information presented allows.