The correct amount is $18,000, the amount that crossed the teller window. Although it undermines the value of the CTR as a tracer document, the other figure would be the result of offsetting a cash in against a cash out; i.e. that's the net amount. The transaction amount was $18,000. A call to the FinCEN Helpline will verify the answer.
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.